Check for NULL pane window in wxAuiManager.

Check that the AUI pane has a non-NULL associated frame before checking
whether it's shown.

This should fix a crash which could happen when docking an undocked toolbar.

Closes #10926.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@67741 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/aui/framemanager.cpp

@@ -3346,7 +3346,8 @@ void wxAuiManager::ShowHint(const wxRect& rect)
             wxAuiPaneInfo& pane = m_panes.Item(i);
 
             if (pane.IsFloating() &&
-                pane.frame->IsShown())
+                    pane.frame &&
+                        pane.frame->IsShown())
             {
                 wxRect rect = pane.frame->GetRect();
 #ifdef __WXGTK__