Avoid bogus context menu events in wxGTK wxDataViewCtrl

Right clicking on the column header shouldn't generate context menu
events, but it did because our gtk_dataview_button_press_callback() got
these events for both the "bin" window, containing the items, and the
"header" window.

Fix this by filtering out the events not sent to the right window.

It would be even better to not get these events in the first place, i.e.
somehow not connect to them in the first place, but it's not clear how
to do this, so settle for this solution for now.

For testing this fix, just right click any column in the dataview
sample: previously this generated both messages about the column header
right click and the context menu in wxGTK, while now it only generates
the former, as in the generic version.

src/gtk/dataview.cpp

@@ -4664,6 +4664,13 @@ gtk_dataview_button_press_callback( GtkWidget *WXUNUSED(widget),
     {
         GtkTreeView* const treeview = GTK_TREE_VIEW(dv->GtkGetTreeView());
 
+        // Surprisingly, we can get the events not only from the "bin" window,
+        // containing the items, but also from the window containing the column
+        // headers, and we're not interested in them here, we already generate
+        // wxEVT_DATAVIEW_COLUMN_HEADER_RIGHT_CLICK for them, so just ignore.
+        if (gdk_event->window != gtk_tree_view_get_bin_window(treeview))
+            return FALSE;
+
         wxGtkTreePath path;
         GtkTreeViewColumn *column = NULL;
         gint cell_x = 0;