Allow setting icon before m_widget is valid.

There is no need to require a valid m_widget,
the "realize" handler will take care of things later.
Closes #16731


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@78270 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/toplevel.cpp

@@ -1387,14 +1387,12 @@ void wxTopLevelWindowGTK::SetTitle( const wxString &title )
 
 void wxTopLevelWindowGTK::SetIcons( const wxIconBundle &icons )
 {
-    wxASSERT_MSG( (m_widget != NULL), wxT("invalid frame") );
-
     base_type::SetIcons(icons);
 
     // Setting icons before window is realized can cause a GTK assertion if
     // another TLW is realized before this one, and it has this one as it's
     // transient parent. The life demo exibits this problem.
-    if (gtk_widget_get_realized(m_widget))
+    if (m_widget && gtk_widget_get_realized(m_widget))
     {
         GList* list = NULL;
         for (size_t i = icons.GetIconCount(); i--;)