Fix "webroot not found" when installed to the root of the webserver

Signed-off-by: Robin Appelman <robin@icewind.nl>

lib/private/Template/CSSResourceLocator.php

@@ -119,7 +119,7 @@ class CSSResourceLocator extends ResourceLocator {
 			if (!$webRoot) {
 				$webRoot = $this->findWebRoot($root);
 
-				if (!$webRoot) {
+				if ($webRoot === null) {
 					$webRoot = '';
 					$this->logger->error('ResourceLocator can not find a web root (root: {root}, file: {file}, webRoot: {webRoot}, throw: {throw})', [
 						'app' => 'lib',

lib/private/Template/ResourceLocator.php

@@ -139,7 +139,7 @@ abstract class ResourceLocator {
 			$tmpRoot = dirname($tmpRoot);
 		}
 
-		if (!$webRoot) {
+		if ($webRoot === null) {
 			$realpath = realpath($root);
 
 			if ($realpath && ($realpath !== $root)) {
@@ -168,10 +168,10 @@ abstract class ResourceLocator {
 			return;
 		}
 
-		if (!$webRoot) {
+		if ($webRoot === null) {
 			$webRoot = $this->findWebRoot($root);
 
-			if (!$webRoot) {
+			if ($webRoot === null) {
 				$webRoot = '';
 				$this->logger->error('ResourceLocator can not find a web root (root: {root}, file: {file}, webRoot: {webRoot}, throw: {throw})', [
 					'app' => 'lib',