fix: Launchpad crashes.

[robertkill]

When there is only one application in the group and it is dragged and dropped within the same group, the drag and drop process is not handled.

log: as title
issue: linuxdeepin/developer-center#8384

[deepin-ci-robot]

deepin pr auto review

关键摘要:

• 在ItemArrangementProxyModel::commitDndOperation函数中，增加了对源文件夹和目标文件夹是否相同的判断，避免了重复移除项目item的操作。
• 新增了ItemsPage::itemCount函数，用于计算总项目数量，提高了代码的可读性和性能。

是否建议立即修改:

• 否，提交中的更改已经包括了一些改进，没有紧急需要修改的问题。但是，建议进行以下几点改进：
  • 确保所有新增加的逻辑都经过了充分的测试，特别是对于文件夹操作和项目移动的测试。
  • 检查是否有必要对ItemsPage::itemCount函数进行优化，例如使用静态编译指令或者缓存结果以提高性能。
  • 考虑对ItemArrangementProxyModel::commitDndOperation函数中的多次重复调用进行优化，例如通过缓存或早返回结果来减少不必要的循环。

[deepin-ci-robot]

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This pull-request has been approved by: BLumia, robertkill

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