Fixes #1991: regression in index.php handling

framework/web/Request.php

@@ -584,9 +584,7 @@ class Request extends \yii\base\Request
 			throw new InvalidConfigException('Unable to determine the path info of the current request.');
 		}
 
-		if ($pathInfo === '/') {
-			$pathInfo = '';
-		} else if ($pathInfo[0] === '/') {
+		if ($pathInfo[0] === '/') {
 			$pathInfo = substr($pathInfo, 1);
 		}
 

framework/web/UrlManager.php

@@ -214,7 +214,7 @@ class UrlManager extends Component
 				}
 			}
 
-			return [$pathInfo, []];
+			return [(string)$pathInfo, []];
 		} else {
 			Yii::trace('Pretty URL not enabled. Using default URL parsing logic.', __METHOD__);
 			$route = $request->get($this->routeVar);