Fix wxWindow::IsDescendant() to work with argument equal to this window.

Passing the window itself as IsDescendant() argument for a top level window
resulted in a NULL pointer dereference. Fix this and also simplify the
function code by not using the parent window before checking it's !NULL.

Closes #14387.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71702 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/wincmn.cpp

@@ -1268,15 +1268,14 @@ bool wxWindowBase::IsDescendant(wxWindowBase* win) const
     // Iterate until we find this window in the parent chain or exhaust it.
     while ( win )
     {
-        wxWindow* const parent = win->GetParent();
-        if ( parent == this )
+        if ( win == this )
             return true;
 
         // Stop iterating on reaching the top level window boundary.
-        if ( parent->IsTopLevel() )
+        if ( win->IsTopLevel() )
             break;
 
-        win = parent;
+        win = win->GetParent();
     }
 
     return false;