pkg_editor: do not ignore failure to create directory

[pcolberg]

Resolves Coverity error "Unchecked return value from library (CHECKED_RETURN)".

[pcolberg]

@IlanTruanovsky This was a first attempt at properly handling failures of mkdir/CreateDirectory. As you can see, however, this adds quite a bit of code including string buffer handling that itself can be a new source of bugs. I have since come to the conclusion that ignoring a failure to create the directory is a pragmatic solution; this will simply delay the failure to the first attempt of creating a file in the (not) newly created directory.

If you submit a pull request for this, you can simply ignore the return value with (void)mkdir(…) and expand the in-code comment to explain why this is a pragmatic solution (to avoid error-prone, platform-dependent error handling).

Taking a step back, cross-platform filesystem operations including proper error handling are nowadays provided in the C++17 filesystem library. However, so far we have not been able to make use of it since our minimum GCC version does not provide <filesystem>; it was only available as an experimental extension.

[pcolberg]

Superseded by #247.