Fix incorrect sending of HTTP error response through Websocket connections.

src/output/output_http.cpp

@@ -43,9 +43,11 @@ namespace Mist {
   }
   
   void HTTPOutput::onFail(){
+    if (!webSock){
       H.Clean(); //make sure no parts of old requests are left in any buffers
       H.SetBody("Stream not found. Sorry, we tried.");
       H.SendResponse("404", "Stream not found", myConn);
+    }
     Output::onFail();
   }