Don't reset previous window event handler in PopEventHandler().

This is harmless but also useless as the previous event handler of a wxWindow
is always NULL anyhow, so simply don't do this. This is consistent with
PushEventHandler() which doesn't call SetPreviousHandler() for the window
itself neither.

Closes #14353.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71621 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/wincmn.cpp

@@ -1439,6 +1439,10 @@ wxEvtHandler *wxWindowBase::PopEventHandler(bool deleteHandler)
         "the first handler of the wxWindow stack should have non-NULL next handler" );
 
     firstHandler->SetNextHandler(NULL);
+
+    // It is harmless but useless to unset the previous handler of the window
+    // itself as it's always NULL anyhow, so don't do this.
+    if ( secondHandler != this )
         secondHandler->SetPreviousHandler(NULL);
 
     // now firstHandler is completely unlinked; set secondHandler as the new window event handler