insertIfNotExists() for storage insertion

lib/private/files/cache/storage.php

@@ -35,9 +35,15 @@ class Storage {
 		if ($row = $result->fetchRow()) {
 			$this->numericId = $row['numeric_id'];
 		} else {
-			$sql = 'INSERT INTO `*PREFIX*storages` (`id`) VALUES(?)';
-			\OC_DB::executeAudited($sql, array($this->storageId));
-			$this->numericId = \OC_DB::insertid('*PREFIX*storages');
+			$connection = \OC_DB::getConnection();
+			if ($connection->insertIfNotExist('*PREFIX*storages', ['id' => $this->storageId])) {
+				$this->numericId = \OC_DB::insertid('*PREFIX*storages');
+			} else {
+				$result = \OC_DB::executeAudited($sql, array($this->storageId));
+				if ($row = $result->fetchRow()) {
+					$this->numericId = $row['numeric_id'];
+				}
+			}
 		}
 	}