fix: infofile add extension name first

[cokemine]

This PR should fix: #982
I can confirm this issue both happens on Linux and Windows.

The arg of PixivHelper.sanitize_filename() should have a extname for info file otherwise trailing dots and spaces from the title will be removed, which is not as expected.

[biggestsonicfan]

I'm not too familiar with what's happening in this exact code, but is there a reason pathlib isn't being used to handle this?

[NewUserHa]

indeed should use PurePath.stem to trim the last dot in the filename to avoid more issues.

[cokemine]

indeed should use PurePath.stem to trim the last dot in the filename to avoid more issues.

I wonder why we have to trim last dots ? All info file should have a ext name .txt or .json
....txt both valid on Windows and Linux

[NewUserHa]

The arg of PixivHelper.sanitize_filename() should have a extname for info file otherwise trailing dots and spaces from the title will be removed, which is not as expected.

Isn't the PR trying to trim the last dot of the filename without the suffix?

I currently didn't encounter any issues with the default filename template. How can [:-8] be right for the default filename template?

[cokemine]

The arg of PixivHelper.sanitize_filename() should have a extname for info file otherwise trailing dots and spaces from the title will be removed, which is not as expected.

Isn't the PR trying to trim the last dot of the filename without the suffix?

I currently didn't encounter any issues with the default filename template. How can [:-8] be right for the default filename template?

I don't think it's needed to trim the suffix dots if the file has an explicit extension name (.txt or .json)

Before this PR, . from image title are trimed. This is because it is passed into PixivHelper.sanitize_filename() without the extension.(info file) I added a fake extension .infoext to circumvent this, and then write the file with the correct extension.

But for image file, The argument of PixivHelper.sanitize_filename() containing the corrent extension name of the image, so . won't be trimed

I think PurePath.stem has the same effect, but the fake extension I set is a fixed length, so I didn't use it