Updater: Check for write permissions in directory of Updater.exe.

[AdmiralCurtiss]

ie, don't blindly assume working directory is directory Updater.exe is in.

This should fix the weird issue where a chain of Dolphin.exe -> Updater.exe -> Dolphin.exe -> Updater.exe requests UAC because it tries to open Updater.log in C:\Windows\System32 (which is the working directory inherited from the permissions downgrade via explorer.exe).

Technically the arguments could request a different path to write the update to, but that shouldn't really happen in practice I think...?

[shuffle2]

maybe the MessageBox calls in this file can be changed to UI::Error?

I think the filename used for permission check should be changed to something else and then deleted (FILE_FLAG_DELETE_ON_CLOSE). Updater.log is actually stored in dolphin's user/Logs folder, and not next to the binary - so having two files named the same yet used for different purposes is confusing.

[AdmiralCurtiss]

Like that?

[shuffle2]

basically yes. could be like this tho:

const auto test_fh = CreateFileW(
      std::filesystem::path(*path).replace_filename("directory_writable_check.tmp").c_str(),
      GENERIC_WRITE, 0, nullptr, CREATE_ALWAYS, FILE_ATTRIBUTE_TEMPORARY | FILE_FLAG_DELETE_ON_CLOSE,
      nullptr);