Fix two issues with Websocket (#472)

* Websocket were always marked as "want_write" (even if they only
  want to read, or worse want nothing).
* Websocket FD was read twice in some case (when socket recv queue was
  larger that size read by libwebsocket)

Signed-off-by: Pierre Fersing <pierre.fersing@bleemeo.com>

src/loop.c

@@ -525,6 +525,12 @@ static void loop_handle_reads_writes(struct mosquitto_db *db, struct pollfd *pol
 		if(context->pollfd_index < 0){
 			continue;
 		}
+#ifdef WITH_WEBSOCKETS
+		if(context->wsi){
+			// Websocket are already handled above
+			continue;
+		}
+#endif
 
 #ifdef WITH_TLS
 		if(pollfds[context->pollfd_index].revents & POLLIN ||

src/websockets.c

@@ -593,7 +593,7 @@ static int callback_http(struct libwebsocket_context *context,
 		case LWS_CALLBACK_DEL_POLL_FD:
 		case LWS_CALLBACK_CHANGE_MODE_POLL_FD:
 			HASH_FIND(hh_sock, db->contexts_by_sock, &pollargs->fd, sizeof(pollargs->fd), mosq);
-			if(mosq){
+			if(mosq && (pollargs->events & POLLOUT)){
 				mosq->ws_want_write = true;
 			}
 			break;