xwayland: Avoid forwarding spurious mouse events

pointerEvents contain all motion events, the xwayland filter is only
concerned with forwarding clicks. Right now we would update an invalid
button state constantly. It did nothing harmful but was still a bit
silly.

src/xwayland/xwayland.cpp

@@ -404,6 +404,9 @@ public:
         if (!m_filterMouse || (window && window->isLockScreen())) {
             return;
         }
+        if (event->type() != QEvent::MouseButtonPress && event->type() != QEvent::MouseButtonRelease) {
+            return;
+        }
 
         auto pointer = waylandServer()->seat()->pointer();
         auto surface = pointer->focusedSurface();