Crash on some notifications

[haringsrob]

Sometimes when a new message comes in into a channel that has not yet been fetched, an error can occur.

Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0   com.haringsbe.collabapp       	0x000000010dc2ac0c specialized static ChannelController.getTextForMessage(_:) + 2828 (ChannelController.swift:57)
1   com.haringsbe.collabapp       	0x000000010dc3200f specialized SlackWebSocketClient.websocketDidReceiveMessage(socket:text:) + 1455 (SlackWebSocketClient.swift:74)
2   com.haringsbe.collabapp       	0x000000010dc2fc0f protocol witness for WebSocketDelegate.websocketDidReceiveMessage(socket:text:) in conformance SlackWebSocketClient + 15
3   org.cocoapods.Starscream      	0x000000010e1638df closure #1 in WebSocket.processResponse(_:) + 191
4   org.cocoapods.Starscream      	0x000000010e172079 partial apply for closure #1 in WebSocket.processResponse(_:) + 25
5   org.cocoapods.Starscream      	0x000000010e15a9b0 thunk for @escaping @callee_guaranteed () -> () + 32
6   libdispatch.dylib             	0x00007fff598add4f _dispatch_call_block_and_release + 12
7   libdispatch.dylib             	0x00007fff598aedcb _dispatch_client_callout + 8
8   libdispatch.dylib             	0x00007fff598b9f5f _dispatch_main_queue_callback_4CF + 1125
9   com.apple.CoreFoundation      	0x00007fff2c865147 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 9
10  com.apple.CoreFoundation      	0x00007fff2c864856 __CFRunLoopRun + 2335
11  com.apple.CoreFoundation      	0x00007fff2c863ce4 CFRunLoopRunSpecific + 463
12  com.apple.HIToolbox           	0x00007fff2bafd895 RunCurrentEventLoopInMode + 293
13  com.apple.HIToolbox           	0x00007fff2bafd5cb ReceiveNextEventCommon + 618
14  com.apple.HIToolbox           	0x00007fff2bafd348 _BlockUntilNextEventMatchingListInModeWithFilter + 64
15  com.apple.AppKit              	0x00007fff29dba95b _DPSNextEvent + 997
16  com.apple.AppKit              	0x00007fff29db96fa -[NSApplication(NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue:] + 1362
17  com.apple.AppKit              	0x00007fff29db375d -[NSApplication run] + 699
18  com.apple.AppKit              	0x00007fff29da2e97 NSApplicationMain + 780
19  com.haringsbe.collabapp       	0x000000010dc184c9 main + 9 (AppDelegate.swift:4)
20  libdyld.dylib                 	0x00007fff598fd085 start + 1

[haringsrob]

Fixed, just have to make a new release.