Stop delivering messages when drop has occurred.

Task-number: QTBUG-27406

Change-Id: If14c108060ad6de70991658f0e0249eb544b87a0
Reviewed-by: Samuel Rødal <samuel.rodal@digia.com>

src/plugins/platforms/xcb/qxcbdrag.cpp

@@ -484,6 +484,12 @@ void QXcbDrag::move(const QMouseEvent *me)
 void QXcbDrag::drop(const QMouseEvent *event)
 {
     QBasicDrag::drop(event);
+
+    if (heartbeat != -1) {
+        killTimer(heartbeat);
+        heartbeat = -1;
+    }
+
     if (!current_target)
         return;
 

src/plugins/platforms/xcb/qxcbdrag.h

@@ -143,7 +143,7 @@ private:
     xcb_window_t current_proxy_target;
 
     QXcbScreen *current_screen;
-
+    // timer used when target wants "continuous" move messages (eg. scroll)
     int heartbeat;
 
     QVector<xcb_atom_t> drag_types;