GameActionManager now performs delayed updates on main thread (#364)

linked crash reports
- Xcode Organizer
  - Crash report batch #1, consisting of 4 crash reports from a single
    device (an iPhone 8) running iOS 14.4.
- Crashlytics
  - Crash report batch #2, consisting of 1 crash report from an iPhone 8
    device running iOS 14.4.

all crashes occurred in method updateNavigationBarWidths of
NavigationBarControllerPhonePortraitOnly, on this line:
  [self.view removeConstraints:constraintsToRemove];

src/play/gameaction/GameActionManager.m

@@ -678,6 +678,11 @@ - (void) delayedUpdate
 {
   if ([LongRunningActionCounter sharedCounter].counter > 0)
     return;
+  if ([NSThread currentThread] != [NSThread mainThread])
+  {
+    [self performSelectorOnMainThread:@selector(delayedUpdate) withObject:nil waitUntilDone:YES];
+    return;
+  }
   [self updateVisibleStates];
   [self updateEnabledStates];
   [self updateScoringMode];