Fixed dangling pointer bug

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_8_BRANCH@49063 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/aui/framemanager.cpp

@@ -2292,6 +2292,8 @@ void wxAuiManager::GetDockSizeConstraint(double* width_pct, double* height_pct)
 
 void wxAuiManager::Update()
 {
+    m_hover_button = NULL;
+
     wxSizer* sizer;
     int i, pane_count = m_panes.GetCount();