fix: clear *pprocess when file copy fails in DocumentFactory::getDocument

[add-uos]

问题

reader/document/Model.cpp:160 的 QFile::copy(targetDoc) 失败分支返回 nullptr 并置 error = ConvertFailed，但 *pprocess 未置空。函数其余全部错误分支（:188/:194/:201/:229/:235/:263/:269/:278/:284）均在返回前置 *pprocess = nullptr，成功路径亦有赋值——该分支是唯一破坏出口参数约定的。实测混合跑中 *process 残留调用方原值（非空），依赖 *process == nullptr 判断的调用方会误判（当前 PageRenderThread.cpp:859 恰好预置了 nullptr 故未实际崩溃，属低危契约缺陷）。

修复

失败分支 return nullptr 前补 *pprocess = nullptr;，与其余错误分支语义对齐。

背景

该问题由 AI 辅助单测（PMS 缺陷热点回归，BUG332133 用例运行时发现）。

Summary by Sourcery

Bug Fixes:

• Clear the process output parameter when document file copying fails, keeping failure behavior consistent with all other error paths.

[sourcery-ai]

Sorry @add-uos, you've used your own review budget of 250,000 diff characters for the last 7 days.

You can request another review in 4 days and 22 hours by commenting @sourcery-ai review. Upgrade to get a review now.

[deepin-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: add-uos

The full list of commands accepted by this bot can be found here.

Details

Needs approval from an approver in each of these files:

• debian/deepin/OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Fixes DocumentFactory::getDocument so a failed document file copy clears *pprocess before returning, preventing callers from observing stale process state.

File-Level Changes

Change	Details	Files
Aligns the file-copy failure path with the function’s output-parameter cleanup contract.	Sets the process output pointer to nullptr before returning on copy failure. Preserves the existing ConvertFailed error and nullptr document return behavior.	reader/document/Model.cpp

---

Tips and commands

Interacting with Sourcery

• Trigger a new review: Comment @sourcery-ai review on the pull request.
• Continue discussions: Reply directly to Sourcery's review comments.
• Generate a GitHub issue from a review comment: Ask Sourcery to create an
  issue from a review comment by replying to it. You can also reply to a
  review comment with @sourcery-ai issue to create an issue from it.
• Generate a pull request title: Write @sourcery-ai anywhere in the pull
  request title to generate a title at any time. You can also comment
  @sourcery-ai title on the pull request to (re-)generate the title at any time.
• Generate a pull request summary: Write @sourcery-ai summary anywhere in
  the pull request body to generate a PR summary at any time exactly where you
  want it. You can also comment @sourcery-ai summary on the pull request to
  (re-)generate the summary at any time.
• Generate reviewer's guide: Comment @sourcery-ai guide on the pull
  request to (re-)generate the reviewer's guide at any time.
• Resolve all Sourcery comments: Comment @sourcery-ai resolve on the
  pull request to resolve all Sourcery comments. Useful if you've already
  addressed all the comments and don't want to see them anymore.
• Dismiss all Sourcery reviews: Comment @sourcery-ai dismiss on the pull
  request to dismiss all existing Sourcery reviews. Especially useful if you
  want to start fresh with a new review - don't forget to comment
  @sourcery-ai review to trigger a new review!

Customizing Your Experience

Access your dashboard to:

• Enable or disable review features such as the Sourcery-generated pull request
  summary, the reviewer's guide, and others.
• Change the review language.
• Add, remove or edit custom review instructions.
• Adjust other review settings.

Getting Help

• Contact our support team for questions or feedback.
• Visit our documentation for detailed guides and information.
• Keep in touch with the Sourcery team by following us on X/Twitter, LinkedIn or GitHub.