Fix: Empty lines in URL_config.ini cause top-most records to be silently deleted

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📜 标题（Title）

请提供这个Pull Request中提议的更改的简洁描述：

• Fix: Empty lines in URL_config.ini cause top-most records to be silently deleted

🔍 描述（Description）

请描述这个PR做了什么/为什么这些更改是必要的：

• When URL_config.ini contains empty lines (e.g., used to visually separate platform categories), the program reads them as \n. In main.py, the delete_line() method incorrectly uses substring matching (del_line in txt_line) to check for deletion.
• Since the newline character \n is present in every line, this logic evaluates to True for the very first line of the configuration file. As a result, every empty line causes the top-most valid URL configuration to be wrongly and silently deleted.
• This PR changes the substring matching to exact matching (del_line == txt_line), which perfectly resolves the data loss issue without any side effects.

📝 类型（Type of Change）

这个PR引入了哪种类型的更改？（请勾选所有适用的选项）

• 修复Bug
• 新功能
• 代码风格更新（格式化，局部变量）
• 重构（改进代码结构）
• 构建相关更改（依赖项，构建脚本等）
• 其他：请描述

🏗️ 测试（Testing）

请描述您已经进行的测试：

• Tested locally with multiple empty lines and duplicate entries in URL_config.ini. Verified that valid stream URLs are no longer deleted and duplicates are correctly removed.

如果适用，请提供测试更改的说明：

• Add empty lines to config/URL_config.ini and run the script. The script should not delete the topmost valid configurations anymore.

📋 检查清单（Checklist）

在您创建这个PR之前，请确保以下所有框都被勾选，方法是在每个框中放置一个x：

• 我已经阅读了贡献指南文档
• 我的更改没有产生新的警告
• 我已经添加了覆盖我更改的测试
• 我已经相应地更新了文档（如果适用）
• 我遵循了这个项目的代码风格

注意： 这个PR在所有复选框被勾选之前不会被合并。

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