Use proper format in wxGTK clipboard selection handler.

For some incomprehensible reason, GDK_SELECTION_TYPE_STRING was hard coded for
all non-text formats even though it was clearly never the right format to use.
Use the correct value specified by the format instead.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72160 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/clipbrd.cpp

@@ -328,7 +328,7 @@ selection_handler( GtkWidget *WXUNUSED(widget),
     {
         gtk_selection_data_set(
             selection_data,
-            GDK_SELECTION_TYPE_STRING,
+            format.GetFormatId(),
             8*sizeof(gchar),
             (const guchar*)buf.data(),
             size );