Do not react to the update hook when the updated node is a folder

- At least Nextcloud 12 emits the updated signals for folders when the Gallery app creates folder thumbnails. This caused lot of warning being printed to the log output when Scanner noticed that the passed in object was not a file.

hooks/filehooks.php

@@ -45,13 +45,15 @@ public static function deleted($node){
 	 * @param \OCP\Files\Node $node pointing to the file
 	 */
 	public static function updated($node){
-		$app = new Music();
-
-		$container = $app->getContainer();
-		$scanner = $container->query('Scanner');
-		$userId = $container->query('UserId');
-		$userFolder = $container->query('UserFolder');
-		$scanner->update($node, $userId, $userFolder);
+		// we are interested only about updates on files, not on folders
+		if ($node->getType() == FileInfo::TYPE_FILE) {
+			$app = new Music();
+			$container = $app->getContainer();
+			$scanner = $container->query('Scanner');
+			$userId = $container->query('UserId');
+			$userFolder = $container->query('UserFolder');
+			$scanner->update($node, $userId, $userFolder);
+		}
 	}
 
 	public function register() {