Initialize YmqIsFifo (#12720)

Author: qyryq

ydb/core/http_proxy/http_req.h

@@ -57,8 +57,8 @@ struct THttpResponseData {
     NJson::TJsonValue Body;
     TString ErrorText{"OK"};
     TString YmqStatusCode;
-    ui32 YmqHttpCode;
-    bool YmqIsFifo;
+    ui32 YmqHttpCode = 500;
+    bool YmqIsFifo = false;
 
     TString DumpBody(MimeTypes contentType);
 };