tdf#117713 set a tiny default size-request for the fixed container

otherwise we get a default one if SetMinClientSize is never called, which
is the case for these spawned-from-basic dialogs

Change-Id: I4f0389de6abcb1e99b32798969dca49bf8f0f760
Reviewed-on: https://gerrit.libreoffice.org/67063
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

vcl/unx/gtk3/gtk3gtkframe.cxx

@@ -1009,6 +1009,7 @@ void GtkSalFrame::InitCommon()
     // add the fixed container child,
     // fixed is needed since we have to position plugin windows
     m_pFixedContainer = GTK_FIXED(g_object_new( ooo_fixed_get_type(), nullptr ));
+    gtk_widget_set_size_request(GTK_WIDGET(m_pFixedContainer), 1, 1);
     gtk_container_add( GTK_CONTAINER(m_pEventBox), GTK_WIDGET(m_pFixedContainer) );
 
     GtkWidget *pEventWidget = getMouseEventWidget();