Support querying whether an extension has been requested

* xcb.el (xcb:got-extension-data-p): New function.

Author: medranocalvo

xcb.el

@@ -523,6 +523,10 @@ classes of EVENT (since they have the same event number)."
             (plist-put (slot-value obj 'extension-plist) namespace sequence))
       (xcb:flush obj))))
 
+(cl-defmethod xcb:got-extension-data-p ((obj xcb:connection) namespace)
+  "Return non-nil when the connection OBJ has extension data for NAMESPACE."
+  (plist-get (slot-value obj 'extension-plist) namespace))
+
 (cl-defmethod xcb:generate-id ((obj xcb:connection))
   "Generate new X ID."
   (let* ((setup (xcb:get-setup obj))