restart BTLE after backgrounding

[IvanSeleznevSpb]

Internal/NewNode has a startNearby() method that calls Bluetooth.bluetoothOn() -> Bluetooth.startServer() -> Bluetooth.tryStartServer() -> BluetoothManager.openGattServer(). https://github.com/clostra/newnode/blob/44f48fe824592987d2025a019b2c1e3dcd4a5693/android/src/main/java/com/clostra/newnode/internal/Bluetooth.java#L265 The startNearby() method is called in onActivityResumed() which causes a new BluetoothGattServer to be created each time a new activity is opened. https://github.com/clostra/newnode/blob/44f48fe824592987d2025a019b2c1e3dcd4a5693/android/src/main/java/com/clostra/newnode/internal/NewNode.java#L623 It works fine a few times (usually 1 or 3 times), and then openGattServer() starts returning null, which results in the exception described above. Before returning null, the openGattServer() method runs for a long time and does it on the main thread, which causes the interface to freeze.

Bluetooth                           com.newnode.messenger      E  startServer
                                                                  java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.bluetooth.BluetoothGattServer.addService(android.bluetooth.BluetoothGattService)' on a null object reference
                                                                  	at com.clostra.newnode.internal.Bluetooth.tryStartServer(Bluetooth.java:280)
                                                                  	at com.clostra.newnode.internal.Bluetooth.startServer(Bluetooth.java:288)
                                                                  	at com.clostra.newnode.internal.Bluetooth.bluetoothOn(Bluetooth.java:142)
                                                                  	at com.clostra.newnode.internal.NewNode.startNearby(NewNode.java:590)
                                                                  	at com.clostra.newnode.internal.NewNode.onActivityResumed(NewNode.java:622)
                                                                  	at android.app.Application.dispatchActivityResumed(Application.java:450)
                                                                  	at android.app.Activity.dispatchActivityResumed(Activity.java:1482)
                                                                  	at android.app.Activity.onResume(Activity.java:2043)
                                                                  	at androidx.fragment.app.FragmentActivity.onResume(FragmentActivity.java:455)
                                                                  	at com.clostra.nnm.BaseActivity.onResume(BaseActivity.java:46)
                                                                  	at com.clostra.nnm.PassphraseRequiredActivity.onResume(PassphraseRequiredActivity.java:78)
                                                                  	at com.clostra.nnm.conversation.ConversationActivity.onResume(ConversationActivity.java:508)
                                                                  	at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1531)
                                                                  	at android.app.Activity.performResume(Activity.java:8734)
                                                                  	at android.app.ActivityThread.performResumeActivity(ActivityThread.java:5351)
                                                                  	at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:5444)
                                                                  	at android.app.servertransaction.ResumeActivityItem.execute(ResumeActivityItem.java:54)
                                                                  	at android.app.servertransaction.ActivityTransactionItem.execute(ActivityTransactionItem.java:45)
                                                                  	at android.app.servertransaction.TransactionExecutor.executeLifecycleState(TransactionExecutor.java:176)
                                                                  	at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:97)
                                                                  	at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2574)
                                                                  	at android.os.Handler.dispatchMessage(Handler.java:106)
                                                                  	at android.os.Looper.loopOnce(Looper.java:226)
                                                                  	at android.os.Looper.loop(Looper.java:313)
                                                                  	at android.app.ActivityThread.main(ActivityThread.java:8757)
                                                                  	at java.lang.reflect.Method.invoke(Native Method)
                                                                  	at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:571)
                                                                  	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1067)