WebSocket must not be established when subprotocol is not selected by the server

Source/modules/websockets/WebSocketHandshake.cpp

Index: Source/modules/websockets/WebSocketHandshake.cpp
diff --git a/Source/modules/websockets/WebSocketHandshake.cpp b/Source/modules/websockets/WebSocketHandshake.cpp
index c2e1ca742af1d2e289d3cf2d3dbe0a44c59aefcb..46e8e9c78da9a8a3075f19da9639a409d9bc561e 100644
--- a/Source/modules/websockets/WebSocketHandshake.cpp
+++ b/Source/modules/websockets/WebSocketHandshake.cpp
@@ -548,6 +548,9 @@ bool WebSocketHandshake::checkResponseHeaders()
             m_failureReason = "Error during WebSocket handshake: Sec-WebSocket-Protocol mismatch";
             return false;
         }
+    } else if (!m_clientProtocol.isEmpty()) {
+        m_failureReason = "Error during WebSocket handshake: Sec-WebSocket-Protocol mismatch";
+        return false;
     }
     return true;
 }