Also had to fix a few of the audacious files to get them to compile, mainly not using NULL in the input plugin constructor and casting the STREAMFILE functions (maybe some *nix compilers would've accepted those, but FreeBSD 12's Clang did not)
It was implemented for Audacious only to open companion NWA files, but
current version has no need for it. In case there is some obscure thing
that needs it, Audacious's vfs.cc should translate or return realnames
transparently, without having to modify other streamfiles.
Handle new VFSFile throwing an error correctly, which requires checking the m_impl status of VFSFile. Conveniently, there's a bool operator on the class exactly for that purpose.
