get rid of the built-in drop target in rich text controls before setting the user-defined one as otherwise it fails

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@48704 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/textctrl.h

@@ -139,6 +139,10 @@ public:
 
     // Implementation from now on
     // --------------------------
+ 
+#if wxUSE_DRAG_AND_DROP && wxUSE_RICHEDIT
+    virtual void SetDropTarget(wxDropTarget *dropTarget);
+#endif // wxUSE_DRAG_AND_DROP && wxUSE_RICHEDIT
 
     virtual void SetWindowStyleFlag(long style);