put assert back to protect against bad logic in frontend drag implementations

render/box_textarea.c

@@ -151,6 +151,10 @@ static void box_textarea_callback(void *data, struct textarea_msg *msg)
 			default:
 				LOG(("Drag type %d not handled.",
 				     msg->data.drag));
+				/* This is a logic faliure in the
+				 * front end code so abort.
+				 */
+				assert(0);
 				break;
 			}
 		}