matchbox-wm:  Fix to support closing windows in multi-touch panels

In many applications, the close is not recognized because the sub window class is NULL
This calculates coordinates to track close touch actions in the area to respond.

Upstream Status: Not applicable

diff --git a/src/client_common.c b/src/client_common.c
index 2b62024..30724c1 100644
--- a/src/client_common.c
+++ b/src/client_common.c
@@ -779,10 +779,24 @@ client_get_button_list_item_from_event(Client *c, XButtonEvent *e)
 {
   struct list_item *l = c->buttons;
   MBClientButton   *b = NULL;
-
+  int dx, dy;
   while (l != NULL)
     {
       b = (MBClientButton *)l->data;
+	  if (e->subwindow == 0)
+	  {
+		dx = (e->x - b->x - b->w/2) > 0 ? \
+			 (e->x - b->x - b->w/2) : \
+			 (b->x + b->w/2 - e->x);
+
+		dy = (e->y - b->y - b->h/2) > 0 ? \
+			 (e->y - b->y - b->h/2) : \
+			 (b->y + b->h/2 - e->y);
+
+		if (dx <= b->w/2 && dy <= b->h/2)
+		  return l;
+	  }
+
       if (b->win == e->subwindow)
 	{
 	  return l;
