fix: if uri is empty string, then it should be /

Make it the same behavior as when URIProtocol is REQUEST_URI.

Author: kenjis

system/HTTP/IncomingRequest.php

@@ -329,7 +329,7 @@ protected function parseQueryString(): string
         $uri = $_SERVER['QUERY_STRING'] ?? @getenv('QUERY_STRING');
 
         if (trim($uri, '/') === '') {
-            return '';
+            return '/';
         }
 
         if (strncmp($uri, '/', 1) === 0) {

tests/system/HTTP/IncomingRequestDetectingTest.php

@@ -155,7 +155,7 @@ public function testPathQueryStringEmpty()
         $_SERVER['QUERY_STRING'] = '';
         $_SERVER['SCRIPT_NAME']  = '/index.php';
 
-        $expected = '';
+        $expected = '/';
         $this->assertSame($expected, $this->request->detectPath('QUERY_STRING'));
     }