Ensure that the hash method does not return null

To match https://github.com/nextcloud/server/blob/beececf66068f57c416225efcde9b44ce5c2e835/lib/private/Files/View.php#L1050

- Fix #44110

Signed-off-by: Louis Chemineau <louis@chmn.me>

lib/private/Files/Storage/Local.php

@@ -399,8 +399,8 @@ public function fopen($path, $mode) {
 		return $result;
 	}
 
-	public function hash($type, $path, $raw = false) {
-		return hash_file($type, $this->getSourcePath($path), $raw);
+	public function hash($type, $path, $raw = false): string|false {
+		return hash_file($type, $this->getSourcePath($path), $raw) ?? false;
 	}
 
 	public function free_space($path) {