attempt to use encoding header for decoding

[finnboeger]

The encoding of some files is getting detected incorrectly. If a character, that gets changed due to a different encoding being used, is present in the audio file path it will lead to a canonicalzation error.

While automatic encoding detection is not something that I will touch with a 10ft pole we can work around this by honoring the #ENCODING header if it is present.
As these chars are always interpreted correctly regardless of the encoding we can decode as ASCII and disregard any invalid bytes. If the header is not present it falls back on the previous auto-detection algorithm.

(Example File that gets misidentified: petit milady - 360° Hoshi no Orchestra (TV).txt)

[finnboeger]

The added test to verify that without the encoding header the file would be misinterpreted is subject to failing if chardet changes. However if we don't test that it fails in absence of the header, we can't be sure that the presence of the header fixed the issue.