Call notifications appear immediately after call

previously you had to leave/return. This happens because we unregister
observers while our view is not visible.

// FREEBIE

Signal/src/view controllers/MessagesViewController.m

@@ -345,6 +345,9 @@ typedef enum : NSUInteger {
 
     [self toggleObservers:YES];
 
+    // Triggering modified notification renders "call notification" when leaving full screen call view
+    [self.thread touch];
+
     // restart any animations that were stopped e.g. while inspecting the contact info screens.
     [[NSNotificationCenter defaultCenter] postNotificationName:OWSMessagesViewControllerDidAppearNotification
                                                         object:nil];