moving the new error check into existing http response error block to…

… reduce the possibility of false positives

client.go

@@ -186,18 +186,6 @@ func (d *Dialer) DialContext(ctx context.Context, urlStr string, requestHeader h
 		return nil, nil, errMalformedURL
 	}
 
-	if d.TLSClientConfig != nil {
-		for _, proto := range d.TLSClientConfig.NextProtos {
-			if proto != "http/1.1" {
-				return nil, nil, fmt.Errorf(
-					"websocket: protocol %q was given but is not supported; "+
-						"sharing tls.Config with net/http Transport can cause this error",
-					proto,
-				)
-			}
-		}
-	}
-
 	req := &http.Request{
 		Method:     http.MethodGet,
 		URL:        u,
@@ -383,6 +371,17 @@ func (d *Dialer) DialContext(ctx context.Context, urlStr string, requestHeader h
 
 	resp, err := http.ReadResponse(conn.br, req)
 	if err != nil {
+		if d.TLSClientConfig != nil {
+			for _, proto := range d.TLSClientConfig.NextProtos {
+				if proto != "http/1.1" {
+					return nil, nil, fmt.Errorf(
+						"websocket: protocol %q was given but is not supported; "+
+							"sharing tls.Config with net/http Transport can cause this error",
+						proto,
+					)
+				}
+			}
+		}
 		return nil, nil, err
 	}