fix: changeCase should not affect prefix

[zotune]

Based on issues:
#779
#780

Description:
There's an issue when using symbols like dot in prefix, ie {fileNameWithoutExt}.

It does not work because Keygen Case style overwrites it:

Without Keygen Case style:

[dfaust]

I had the same issue and fixed it, too.

Unfortunately your solution has two problems.

1. The key prefix is prepended even if it's empty or source.
2. Change case is not applied to the file name.

The following code should work without these issues:

  key = changeCase(key, Config.keygenStyle)

  let keyPrefix = Config.keyPrefix
  if (keyPrefix && keygenStrategy !== 'empty' && keygenStrategy !== 'source') {
    if (filepath && keyPrefix.includes('fileName')) {
      keyPrefix = keyPrefix
        .replace('{fileName}', changeCase(basename(filepath), Config.keygenStyle))
        .replace('{fileNameWithoutExt}', changeCase(basename(filepath, extname(filepath)), Config.keygenStyle))
    }

    key = keyPrefix + key
  }

  key = key.trim()

[zotune]

@dfaust Thank you. Looks good. Should I update this PR with your code changes? (I was unable to test this)

[dfaust]

@zotune Sure, go ahead.

[zotune]

@dfaust Done. Let me know if its okay.

[dfaust]

@zotune Looks good!