Fix #7009: Remove leftover .msi and msi.log after update

[chrip]

Fixes #7009

Ensure leftover Windows installers (.msi) and the msiexec log (msi.log) are removed after updates,
both for internal updater flow and for externally performed (manual) installs.

What I changed

• NSISUpdater::wipeUpdateData() now removes update file and msi.log and logs failures.
• handleStartup() will now call wipeUpdateData() if the update was performed externally.

How to test

1. Case A (internal updater): simulate a download -> run installer via updater -> restart client -> verify .msi and msi.log are removed.
2. Case B (manual install): download .msi to the config path, run it manually to update, start client -> confirm leftover files are removed.
3. Check logs for messages like "Removed updater file" / "Removed msi log file" or warning messages if removal failed.

Notes

• This is a Windows-only fix targeted at issue [Bug]: Updater doesn't clean up installer (.msi) #7009.

Fixes #7009

[Aiiaiiio]

Nice one! Please see my comments as suggestions.

[github-actions]

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[mgallien]

@chrip do you plan to still work in this PR ?
if yes, could you update us on your plans and eventually make it ready for release

[chrip]

The fix I am proposing here is definitely better than the current behavior. In the related issue #7009, there is also the suggestion “Fetching to %TEMP% would be a better option.” I have not implemented this improvement and would not change it before the release. As far as I am concerned, this PR is final.

[mgallien]

some small requests for improvements

[github-actions]

Artifact containing the AppImage: nextcloud-appimage-pr-8980.zip

Digest: sha256:7f3966a005d875bff160720a6e8a109dda8e4882d72d69f270eec391bd97c0ae

To test this change/fix you can download the above artifact file, unzip it, and run it.

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