Fix WebSocketClientHandshaker not generating correct handshake request when path is empty (#10095)

Motivation:

WebSocketClientHandshaker#upgradeUrl doesn't comperly compute relative url when path is empty and produces url such as `?access_token=foo` instead of `/?access_token=foo`.

Modifications:

* fix WebSocketClientHandshaker#upgradeUrl
* add tests for urls without path, with and without query

Result:

WebSocketClientHandshaker properly connects to url without path.

codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocketClientHandshaker.java

@@ -546,12 +546,9 @@ public abstract class WebSocketClientHandshaker {
         }
 
         String path = wsURL.getRawPath();
+        path = path == null || path.isEmpty() ? "/" : path;
         String query = wsURL.getRawQuery();
-        if (query != null && !query.isEmpty()) {
+        return query != null && !query.isEmpty() ? path + '?' + query : path;
-            path = path + '?' + query;
-        }
-
-        return path == null || path.isEmpty() ? "/" : path;
     }
 
     static CharSequence websocketHostValue(URI wsURL) {

codec-http/src/test/java/io/netty/handler/codec/http/websocketx/WebSocketClientHandshakerTest.java

@@ -217,6 +217,30 @@ public abstract class WebSocketClientHandshakerTest {
         }
     }
 
+    @Test
+    public void testUpgradeUrlWithoutPath() {
+        URI uri = URI.create("ws://localhost:9999");
+        WebSocketClientHandshaker handshaker = newHandshaker(uri);
+        FullHttpRequest request = handshaker.newHandshakeRequest();
+        try {
+            assertEquals("/", request.uri());
+        } finally {
+            request.release();
+        }
+    }
+
+    @Test
+    public void testUpgradeUrlWithoutPathWithQuery() {
+        URI uri = URI.create("ws://localhost:9999?a=b%20c");
+        WebSocketClientHandshaker handshaker = newHandshaker(uri);
+        FullHttpRequest request = handshaker.newHandshakeRequest();
+        try {
+            assertEquals("/?a=b%20c", request.uri());
+        } finally {
+            request.release();
+        }
+    }
+
     @Test
     public void testAbsoluteUpgradeUrlWithQuery() {
         URI uri = URI.create("ws://localhost:9999/path%20with%20ws?a=b%20c");