sanitize_str function makes new character appear on Debian Linux

[ghost]

On my side I've downloaded a couple of tracks and I always end up having files with this character

I checked the code and apparently that function was the problem, if I set "replacement_char" to empty the character does not appear, which is how I wanted it
Not sure if its a bug, just pointing that out haha

[7x11x13]

This is intended because it could be the case that a filename is made up of entirely invalid characters for a filename, in which case downloading would fail if the replacement char is "". However, the replacement char should probably be able to be changed by the user via command line argument, so I'll leave this issue open