Bug 1442938: Nil-check the title in nsCocoaWindow::importState / exportState. r=mstange

Looking at the docs for [NSWindow title] I don't think it's supposed to return
nil under any circumstances...

But it does in our automation, for some reason, with the patches for bug 1439875
which make our fullscreen code run a bit earlier.

MozReview-Commit-ID: AX4qzjzsqST

--HG--
extra : rebase_source : a01f2ba6b42b4067e7a4886c4814e85f317a4a6f

widget/cocoa/nsCocoaWindow.mm

@@ -3198,7 +3198,9 @@ static const NSString* kStateCollectionBehavior = @"collectionBehavior";
 
 - (void)importState:(NSDictionary*)aState
 {
-  [self setTitle:[aState objectForKey:kStateTitleKey]];
+  if (NSString* title = [aState objectForKey:kStateTitleKey]) {
+    [self setTitle:title];
+  }
   [self setDrawsContentsIntoWindowFrame:[[aState objectForKey:kStateDrawsContentsIntoWindowFrameKey] boolValue]];
   [self setTitlebarColor:[aState objectForKey:kStateActiveTitlebarColorKey] forActiveWindow:YES];
   [self setTitlebarColor:[aState objectForKey:kStateInactiveTitlebarColorKey] forActiveWindow:NO];
@@ -3209,7 +3211,9 @@ static const NSString* kStateCollectionBehavior = @"collectionBehavior";
 - (NSMutableDictionary*)exportState
 {
   NSMutableDictionary* state = [NSMutableDictionary dictionaryWithCapacity:10];
-  [state setObject:[self title] forKey:kStateTitleKey];
+  if (NSString* title = [self title]) {
+    [state setObject:title forKey:kStateTitleKey];
+  }
   [state setObject:[NSNumber numberWithBool:[self drawsContentsIntoWindowFrame]]
             forKey:kStateDrawsContentsIntoWindowFrameKey];
   NSColor* activeTitlebarColor = [self titlebarColorForActiveWindow:YES];