Account for extension length when truncating filename

[tomasklaen]

I wasn't sure what to do with the filename when extension is loner than maxLength, as removing it completely would create a dotfile which might have unintended consequences, so I decided to keep at least 1 character of the filename in place.

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Also found another bug: filenamify doesn't account for dotfiles, so this test:

t.is(filenamify('.asdfghjkl', {maxLength: 2}), '.asdfghjkl');

Can't pass as other parts of filenamify remove the leading dot as they consider it a relative path, and than truncation later on treats it as a filename.

Separate PR? :)

[sindresorhus]

Separate PR? :)

👍