crashfix: production crash when notification fired before view loaded

We're observing notifications in init that modify the view, which is
problematic if we receive a notification before the view has loaded.

// FREEBIE

Signal/src/ViewControllers/CallViewController.swift

@@ -25,6 +25,7 @@ class CallViewController: OWSViewController, CallObserver, CallServiceObserver,
 
     // MARK: Views
 
+    var isViewLoaded = false
     var hasConstraints = false
     var blurView: UIVisualEffectView!
     var dateFormatter: DateFormatter?
@@ -158,7 +159,9 @@ class CallViewController: OWSViewController, CallObserver, CallServiceObserver,
     }
 
     func didBecomeActive() {
-        shouldRemoteVideoControlsBeHidden = false
+        if (self.isViewLoaded) {
+            shouldRemoteVideoControlsBeHidden = false
+        }
     }
 
     // MARK: View Lifecycle
@@ -195,6 +198,7 @@ class CallViewController: OWSViewController, CallObserver, CallServiceObserver,
         call.addObserverAndSyncState(observer: self)
 
         Environment.getCurrent().callService.addObserverAndSyncState(observer: self)
+        self.isViewLoaded = true
     }
 
     // MARK: - Create Views