core.load() should raise an exception for unsupported files

[ghost]

OS: macos 11.2.3 eyeD3 version: 0.9.7b0

If I have an incompatible file and do the following:

import eyed3
audiofile = eyed3.load("img.png")
audiofile.tag.artist = "abc"
audiofile.tag.save()

The result is:

Traceback (most recent call last):
  File "", line 3, in <module>
    audiofile.tag.artist = "abc"
AttributeError: 'NoneType' object has no attribute 'tag'

I guess it would be better if core.load() would not just return None but raise an exception.

Moreover, if I run eyeD3 with the unsupported file as an argument, I get: No audio files found. It would be better if eyeD3 noticed the user that the file type is unsupported.

[nicfit]

I never considered an mp3 without tag an error, so not exception worthy. The AudioFile object still has useful info about the mp3 itself in the result.