Fix calculating size for empty folders

lib/files/cache/cache.php

@@ -485,16 +485,13 @@ class Cache {
 	 * @return int
 	 */
 	public function calculateFolderSize($path) {
-		$id = $this->getId($path);
-		if ($id === -1) {
-			return 0;
-		}
+		$totalSize = 0;
+		$entry = $this->get($path);
+		if ($entry && $entry['mimetype'] === 'httpd/unix-directory') {
+			$id = $entry['fileid'];
 			$sql = 'SELECT `size` FROM `*PREFIX*filecache` WHERE `parent` = ? AND `storage` = ?';
 			$result = \OC_DB::executeAudited($sql, array($id, $this->getNumericStorageId()));
-		$totalSize = 0;
-		$hasChilds = 0;
 			while ($row = $result->fetchRow()) {
-			$hasChilds = true;
 				$size = (int)$row['size'];
 				if ($size === -1) {
 					$totalSize = -1;
@@ -503,10 +500,10 @@ class Cache {
 					$totalSize += $size;
 				}
 			}
-
-		if ($hasChilds) {
+			if ($entry['size'] !== $totalSize) {
 				$this->update($id, array('size' => $totalSize));
 			}
+		}
 		return $totalSize;
 	}