[http] discard web socket connection without handler

If no any handler was found - http request associated with specified web socket can be directly  discarded.
Connection was established - but was not handled in the ROOT.

(cherry picked from commit 5f57840)

Author: linev

net/http/src/THttpServer.cxx

@@ -1128,8 +1128,10 @@ Bool_t THttpServer::ExecuteWS(std::shared_ptr<THttpCallArg> &arg, Bool_t externa
       return kTRUE;
    }
 
-   if (!handler)
+   if (!handler) {
+      arg->Set404();
       return kFALSE;
+   }
 
    Bool_t process = kFALSE;