Getting a DatabaseException on startup: (database is locked (code 5 SQLITE_BUSY[5]))

## 🐛 Bug Report

Hi, I'm having a DatabaseException on the application's first load, when it tries to setup the database for the cache. The cache stays unusable for this first load, but the second time the application is opened it can work this out and then it will continue working every time.

This is a logcat output from Android:

```
09-05 16:18:26.154 19280 19371 I flutter : error DatabaseException(database is locked (code 5 SQLITE_BUSY[5])) sql 'BEGIN EXCLUSIVE' args [] during open, closing...
09-05 16:18:26.165 19280 19371 E flutter : [ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: DatabaseException(database is locked (code 5 SQLITE_BUSY[5])) sql 'BEGIN EXCLUSIVE' args []
09-05 16:18:26.165 19280 19371 E flutter : #0 wrapDatabaseException (package:sqflite/src/exception_impl.dart:11)
09-05 16:18:26.165 19280 19371 E flutter :
09-05 16:18:26.165 19280 19371 E flutter : #1 SqfliteDatabaseMixin.txnSynchronized (package:sqflite_common/src/database_mixin.dart:465)
09-05 16:18:26.165 19280 19371 E flutter :
09-05 16:18:26.165 19280 19371 E flutter : #2 SqfliteDatabaseMixinExt.txnBeginTransaction (package:sqflite_common/src/database_mixin.dart:353)
09-05 16:18:26.165 19280 19371 E flutter :
09-05 16:18:26.165 19280 19371 E flutter : #3 SqfliteDatabaseMixin.beginTransaction (package:sqflite_common/src/database_mixin.dart:719)
09-05 16:18:26.165 19280 19371 E flutter :
09-05 16:18:26.165 19280 19371 E flutter : #4 SqfliteDatabaseMixinExt._txnTransaction (package:sqflite_common/src/database_mixin.dart:330)
09-05 16:18:26.165 19280 19371 E flutter :
09-05 16:18:26.165 19280 19371 E flutter : #5 BasicLock.synchronized (package:synchronized/src/basic_lock.dart:33)
09-05 16:18:26.165 19280 19371 E flutter :
09-05 16:18:26.165 19280 19371 E flutter : #6 SqfliteDatabaseMixin.txnSynchronized (package:sqflite_common/src/database_mixin.dart:490)
09-05 16:18:26.165 19280 19371 E flutter :
09-05 16:18:26.165 19280 19371 E flutter : #7 SqfliteDatabaseMixin.doOpen (package:sqflite_common/src/database_mixin.dart:939)
09-05 16:18:26.165 19280 19371 E flutter :
09-05 16:18:26.165 19280 19371 E flutter : #8 SqfliteDatabaseOpenHelper.openDatabase (package:sqflite_common/src/database.dart:46)
09-05 16:18:26.165 19280 19371 E flutter :
09-05 16:18:26.165 19280 19371 E flutter : #9 SqfliteDatabaseFactoryMixin.openDatabase. (package:sqflite_common/src/factory_mixin.dart:110)
09-05 16:18:26.165 19280 19371 E flutter :
09-05 16:18:26.165 19280 19371 E flutter : #10 ReentrantLock.synchronized. (package:synchronized/src/reentrant_lock.dart:37)
09-05 16:18:26.165 19280 19371 E flutter :
09-05 16:18:26.165 19280 19371 E flutter : #11 BasicLock.synchronized (package:synchronized/src/basic_lock.dart:33)
09-05 16:18:26.165 19280 19371 E flutter :
09-05 16:18:26.165 19280 19371 E flutter : #12 CacheObjectProvider.open (package:flutter_cache_manager/src/storage/cache_info_repositories/cache_object_provider.dart:30)
09-05 16:18:26.165 19280 19371 E flutter :
09-05 16:18:26.165 19280 19371 E flutter : #13 CacheStore._getCacheDataFromDatabase (package:flutter_cache_manager/src/cache_store.dart:112)
09-05 16:18:26.165 19280 19371 E flutter :
```

At the moment I only tried this on Android, and I'm using version 3.3.1.

My first guess is that some other library may be using Sqlite at the same time, or some other thing like that, but anyways that doesn't seems to be a good reason to crash. Is this issue known?

Thank you

Reproduce the first-load failure on Android with version 3.3.1, then start from CacheObjectProvider.open in package:flutter_cache_manager/src/storage/cache_info_repositories/cache_object_provider.dart and CacheStore._getCacheDataFromDatabase in cache_store.dart. Trace the BEGIN EXCLUSIVE path through sqflite and determine why the cache database is locked during startup; done means the first load opens the cache without an unhandled SQLITE_BUSY exception.

Scritto dal modello di indicizzazione a partire dal testo della issue.