• fix bug: Files filter by keyword "document" will match all folders
• change BackHandler logic: press back button when filter and selection mode both are enabled, will quit selection first

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• 修复文件管理器过滤关键字为"document"时将匹配所有文件夹的bug
• 修改返回键处理逻辑：当过滤模式和选择模式同时开启时，按返回键先退出选择模式