nghttpx: Don't show warning WINDOW_UPDATE failure for HTTP/1 downstream

src/shrpx_http2_downstream_connection.cc

@@ -473,7 +473,11 @@ int Http2DownstreamConnection::resume_read(IOCtrlReason reason)
       }
     }
   }
-  return (rv1 == 0 && rv2 == 0) ? 0 : -1;
+  if(rv1 == 0 && rv2 == 0) {
+    return 0;
+  }
+  DLOG(WARNING, this) << "Sending WINDOW_UPDATE failed";
+  return -1;
 }
 
 int Http2DownstreamConnection::on_read()

src/shrpx_http2_upstream.cc

@@ -905,9 +905,8 @@ ssize_t downstream_data_read_callback(nghttp2_session *session,
   // Send WINDOW_UPDATE before buffer is empty to avoid delay because
   // of RTT.
   if(*eof != 1 &&
-     evbuffer_get_length(body) < SHRPX_HTTP2_UPSTREAM_OUTPUT_UPPER_THRES &&
-     downstream->resume_read(SHRPX_NO_BUFFER) != 0) {
-    DLOG(WARNING, downstream) << "Sending WINDOW_UPDATE failed";
+     evbuffer_get_length(body) < SHRPX_HTTP2_UPSTREAM_OUTPUT_UPPER_THRES) {
+    downstream->resume_read(SHRPX_NO_BUFFER);
   }
   if(nread == 0 && *eof != 1) {
     return NGHTTP2_ERR_DEFERRED;

src/shrpx_http_downstream_connection.cc

@@ -359,7 +359,8 @@ void HttpDownstreamConnection::pause_read(IOCtrlReason reason)
 
 int HttpDownstreamConnection::resume_read(IOCtrlReason reason)
 {
-  return ioctrl_.resume_read(reason) ? 0 : -1;
+  ioctrl_.resume_read(reason);
+  return 0;
 }
 
 void HttpDownstreamConnection::force_resume_read()