don't override non-default cursors in native controls when no wxCursor is set, a regression introduced by r75690

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@75755 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/window.cpp

@@ -3663,7 +3663,8 @@ bool wxWindowGTK::SetCursor( const wxCursor &cursor )
     if (!wxWindowBase::SetCursor(cursor))
         return false;
 
-    GTKUpdateCursor();
+    if (m_cursor.IsOk())
+        GTKUpdateCursor();
 
     return true;
 }