Merge pull request #41 from utopia-php/fix-files-length

Fix files array length

src/Migration/Sources/Appwrite.php

@@ -254,7 +254,7 @@ public function report(array $resources = []): array
                         )['files'];
 
                         $files = array_merge($files, $currentFiles);
-                        $lastFile = $files[count($files) - 1]['$id'];
+                        $lastFile = $files[count($files) - 1]['$id'] ?? null;
 
                         if (count($currentFiles) < 20) {
                             break;