[mob][photos] log number of row in filesDB for debugging perf issues (#3564)

mobile/lib/db/files_db.dart

@@ -1721,6 +1721,8 @@ class FilesDB {
     final result = await db.getAll(
       'SELECT * FROM $filesTable ORDER BY $columnCreationTime DESC',
     );
+    _logger.info("${result.length} rows in filesDB");
+
     final List<EnteFile> files = await Computer.shared()
         .compute(convertToFilesForIsolate, param: {"result": result});