Avoid clearing selection for mouse button up event which is not over an item, see #17547

(cherry picked from commit e9fdda8638)

src/generic/listctrl.cpp

@@ -2441,7 +2441,7 @@ void wxListMainWindow::OnMouse( wxMouseEvent &event )
             evtCtx.SetEventObject(GetParent());
             GetParent()->GetEventHandler()->ProcessEvent(evtCtx);
         }
-        else
+        else if (event.LeftDown())
         {
             // reset the selection and bail out
             HighlightAll(false);