Error on enter in the "TalkableMessagesEditor" window

[brunurd]

[Need reproduction recipe]

Sometimes on enter in the "TalkableMessagesEditor" window it throw a error. I believe it's happen because it's search for a invalid Message id to show in the Sidebar.

Logs - version 2018.2.6f1:

GUI Error: You are pushing more GUIClips than you are popping. Make sure they are balanced)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)

ArgumentException: Getting control 2's position in a group with only 2 controls when doing repaint
Aborting
UnityEngine.GUILayoutGroup.GetNext () (at C:/buildslave/unity/build/Modules/IMGUI/LayoutGroup.cs:117)
UnityEngine.GUILayoutUtility.DoGetRect (System.Single minWidth, System.Single maxWidth, System.Single minHeight, System.Single maxHeight, UnityEngine.GUIStyle style, UnityEngine.GUILayoutOption[] options) (at C:/buildslave/unity/build/Modules/IMGUI/GUILayoutUtility.cs:461)
UnityEngine.GUILayoutUtility.GetRect (System.Single width, System.Single height) (at C:/buildslave/unity/build/Modules/IMGUI/GUILayoutUtility.cs:433)
UnityEditor.EditorGUILayout.Space () (at C:/buildslave/unity/build/Editor/Mono/EditorGUI.cs:8394)
UnityEditor.EditorGUILayout.Separator () (at C:/buildslave/unity/build/Editor/Mono/EditorGUI.cs:8405)
LavaLeak.Diplomata.Editor.Helpers.GUIHelper.Separator () (at Assets/Plugins/Gitman/diplomata/Diplomata/Editor/Helpers/GUIHelper.cs:149)
LavaLeak.Diplomata.Editor.Windows.TalkableMessagesEditor.Sidebar () (at Assets/Plugins/Gitman/diplomata/Diplomata/Editor/Windows/TalkableMessagesEditor.cs:2276)
LavaLeak.Diplomata.Editor.Windows.TalkableMessagesEditor.DrawMessagesEditor () (at Assets/Plugins/Gitman/diplomata/Diplomata/Editor/Windows/TalkableMessagesEditor.cs:374)
LavaLeak.Diplomata.Editor.Windows.TalkableMessagesEditor.OnGUI () (at Assets/Plugins/Gitman/diplomata/Diplomata/Editor/Windows/TalkableMessagesEditor.cs:179)
System.Reflection.MonoMethod.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at <f2e6809acb14476a81f399aeb800f8f2>:0)
Rethrow as TargetInvocationException: Exception has been thrown by the target of an invocation.
System.Reflection.MonoMethod.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at <f2e6809acb14476a81f399aeb800f8f2>:0)
System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) (at <f2e6809acb14476a81f399aeb800f8f2>:0)
UnityEditor.HostView.Invoke (System.String methodName, System.Object obj) (at C:/buildslave/unity/build/Editor/Mono/HostView.cs:295)
UnityEditor.HostView.Invoke (System.String methodName) (at C:/buildslave/unity/build/Editor/Mono/HostView.cs:288)
UnityEditor.HostView.InvokeOnGUI (UnityEngine.Rect onGUIPosition) (at C:/buildslave/unity/build/Editor/Mono/HostView.cs:261)
UnityEditor.DockArea.OldOnGUI () (at C:/buildslave/unity/build/Editor/Mono/GUI/DockArea.cs:392)
UnityEngine.Experimental.UIElements.IMGUIContainer.DoOnGUI (UnityEngine.Event evt, System.Boolean isComputingLayout) (at C:/buildslave/unity/build/Modules/UIElements/IMGUIContainer.cs:238)
UnityEngine.Experimental.UIElements.IMGUIContainer.HandleIMGUIEvent (UnityEngine.Event e) (at C:/buildslave/unity/build/Modules/UIElements/IMGUIContainer.cs:376)
UnityEngine.Experimental.UIElements.IMGUIContainer.DoRepaint (UnityEngine.IStylePainter painter) (at C:/buildslave/unity/build/Modules/UIElements/IMGUIContainer.cs:88)
UnityEngine.Experimental.UIElements.Panel.PaintSubTree (UnityEngine.Event e, UnityEngine.Experimental.UIElements.VisualElement root, UnityEngine.Matrix4x4 offset, UnityEngine.Experimental.UIElements.VisualElement+ClippingOptions clippingOption, UnityEngine.Rect currentGlobalClip) (at C:/buildslave/unity/build/Modules/UIElements/Panel.cs:732)
UnityEngine.Experimental.UIElements.Panel.PaintSubTreeChildren (UnityEngine.Event e, UnityEngine.Experimental.UIElements.VisualElement root, UnityEngine.Matrix4x4 offset, UnityEngine.Experimental.UIElements.VisualElement+ClippingOptions clippingOption, UnityEngine.Rect textureClip) (at C:/buildslave/unity/build/Modules/UIElements/Panel.cs:748)
UnityEngine.Experimental.UIElements.Panel.PaintSubTree (UnityEngine.Event e, UnityEngine.Experimental.UIElements.VisualElement root, UnityEngine.Matrix4x4 offset, UnityEngine.Experimental.UIElements.VisualElement+ClippingOptions clippingOption, UnityEngine.Rect currentGlobalClip) (at C:/buildslave/unity/build/Modules/UIElements/Panel.cs:736)
UnityEngine.Experimental.UIElements.Panel.Repaint (UnityEngine.Event e) (at C:/buildslave/unity/build/Modules/UIElements/Panel.cs:778)
UnityEngine.Experimental.UIElements.UIElementsUtility.DoDispatch (UnityEngine.Experimental.UIElements.BaseVisualElementPanel panel) (at C:/buildslave/unity/build/Modules/UIElements/UIElementsUtility.cs:227)
UnityEngine.Experimental.UIElements.UIElementsUtility.ProcessEvent (System.Int32 instanceID, System.IntPtr nativeEventPtr) (at C:/buildslave/unity/build/Modules/UIElements/UIElementsUtility.cs:74)
UnityEngine.GUIUtility.ProcessEvent (System.Int32 instanceID, System.IntPtr nativeEventPtr) (at C:/buildslave/unity/build/Modules/IMGUI/GUIUtility.cs:171)