Don't use the mapper - all DetachedSong instances we get have already
been mapped.

Merge duplicate code.

Fixes potential nullptr dereference.

Fixes potential nullptr dereference.

This pointer was allocated by libc, not by GLib.

Don't duplicate the buffer just to null-terminate the string.
According to libFLAC API documentation, the string is already
null-terminated.

To replace g_strdup().

Move code from the "mad" plugin.

Move code from the "mad" plugin.

Replaces GLib's g_str_has_prefix().