Avoid resetting global cursor if no global cursor is set

see #17503

(cherry picked from commit 5819b9cbc5)

src/gtk/cursor.cpp

@@ -385,6 +385,9 @@ bool wxIsBusy()
 
 void wxSetCursor( const wxCursor& cursor )
 {
-    g_globalCursor = cursor;
+    //if (cursor.IsOk() || g_globalCursor.IsOk())
-    SetGlobalCursor(cursor);
+    {
+        g_globalCursor = cursor;
+        SetGlobalCursor(cursor);
+    }
 }