Check if Mac QSearchField has focus before handling the notification.

Otherwise, playlist's search field will always handle those shortcuts, and they won't work anywhere else on the same window.
Fixes #3320.

3rdparty/qocoa/qsearchfield_mac.mm

@@ -107,6 +107,13 @@ public:
 
 @implementation QocoaSearchField
 -(BOOL)performKeyEquivalent:(NSEvent*)event {
+
+    // First, check if we have the focus.
+    // If no, it probably means this event isn't for us.
+    NSResponder* firstResponder = [[NSApp keyWindow] firstResponder];
+    if ([firstResponder isKindOfClass:[NSText class]] &&
+            [(NSText*)firstResponder delegate] == self) {
+
         if ([event type] == NSKeyDown && [event modifierFlags] & NSCommandKeyMask)
         {
             QString keyString = toQString([event characters]);
@@ -135,6 +142,7 @@ public:
                 return YES;
             }
         }
+    }
 
     return NO;
 }