support -u2 for proxy

src/proxy.c

@@ -552,6 +552,7 @@ for(;;){
 
 #endif
 
+ if(param->srv->needuser > 1 && !param->username) {RETURN(4);}
  if((res = (*param->srv->authfunc)(param))) {RETURN(res);}
 
  if(ftp && param->redirtype != R_HTTP){