xwayland: zalloc the x11_data_sources

The wrapped weston_data_source struct has new fields which were left
uninitialized, so its access is unreliable.

The data source in xwayland/dnd.c should be eventually setting the
drag-and-drop actions, but it is a lot more incomplete than that
(read: completely), so falls out of the scope of this patch.

Signed-off-by: Carlos Garnacho <carlosg@gnome.org>
diff --git a/xwayland/dnd.c b/xwayland/dnd.c
index a036b30..f17e4cd 100644
--- a/xwayland/dnd.c
+++ b/xwayland/dnd.c
@@ -162,7 +162,7 @@
 	xcb_get_property_cookie_t cookie;
 	xcb_get_property_reply_t *reply;
 
-	source = malloc(sizeof *source);
+	source = zalloc(sizeof *source);
 	if (source == NULL)
 		return;