[release-v2.1] rpcserver: Fix CheckOrigin inverted err check.

When both the `Origin` header and the request `Host` header lack an
explicit port (common behind reverse proxies on standard ports 443/80),
both values collapse to empty string, and `equalASCIIFold("",
"")` returns `true` - allowing **any cross-origin websocket handshake**
to succeed.

Author: davecgh

internal/rpcserver/rpcserver.go

@@ -5964,10 +5964,10 @@ func (s *Server) route(ctx context.Context) *http.Server {
 				// Strip the port from both the origin and request hosts.
 				originHost := originURL.Host
 				requestHost := r.Host
-				if host, _, err := net.SplitHostPort(originHost); err != nil {
+				if host, _, err := net.SplitHostPort(originHost); err == nil {
 					originHost = host
 				}
-				if host, _, err := net.SplitHostPort(requestHost); err != nil {
+				if host, _, err := net.SplitHostPort(requestHost); err == nil {
 					requestHost = host
 				}