macosx: avoid index out of bound exceptions in some cases

(cherry picked from commit 2aa0ad9c3da62df3f31ff317bd747eb0b8524b71)
Signed-off-by: David Fuhrmann <david.fuhrmann@googlemail.com>

modules/gui/macosx/MainWindow.m

@@ -1832,6 +1832,7 @@ static VLCMainWindow *_o_sharedInstance = nil;
 
 - (void)hasBecomeFullscreen
 {
+    if( [[o_video_view subviews] count] > 0 )
         [o_fullscreen_window makeFirstResponder: [[o_video_view subviews] objectAtIndex:0]];
 
     [o_fullscreen_window makeKeyWindow];
@@ -1993,6 +1994,7 @@ static VLCMainWindow *_o_sharedInstance = nil;
     [[o_temp_view superview] replaceSubview:o_temp_view with:o_video_view];
     [o_video_view release];
     [o_video_view setFrame:[o_temp_view frame]];
+    if( [[o_video_view subviews] count] > 0 )
         [[o_video_view window] makeFirstResponder: [[o_video_view subviews] objectAtIndex:0]];
     if( [[o_video_view window] isVisible] )
     {