macosx: when main window is hidden, let playlist menu item only display the window

Furthermore, this commit fixes close button functionality in dark ui style when video is playing
(cherry picked from commit 2709f26e4112d8f1745cec7893efeb45368bb814)
Signed-off-by: David Fuhrmann <david.fuhrmann@googlemail.com>

modules/gui/macosx/MainWindow.m

@@ -634,9 +634,10 @@ static VLCMainWindow *_o_sharedInstance = nil;
 
 - (IBAction)togglePlaylist:(id)sender
 {
-    if (![self isVisible])
+    if (![self isVisible] && sender != nil)
     {
         [self makeKeyAndOrderFront: sender];
+        return;
     }
 
     BOOL b_activeVideo = [[VLCMain sharedInstance] activeVideoPlayback];