They will be stopped by ~EventThread() when the `Instance` is deleted.

Currently it falls back to system default device (either internal speaker or headphone) when device not found. 
I believe it is a better to fail in this case, to make it better aligned with platforms (such as alsa).

Previously, a seek to the end of the file would cause an assertion
failure in SparseMap::Check() because the given offset was invalid.

Closes #453

Must lock the mutex before calling any of the unprotected InputStream methods.

Closes #462

Fixes build failure after commit
0cea67ee

GCC 9's libstdc++ is unable to use forward-declared types as
std::vector item because the compiler wants to resolve `noexcept()` on
the item destructor.

libcdio_paranoia was split from libcdio in version 90, and at the same
time, the header was moved from cdio/paranoia.h to
cdio/paranoia/paranoia.h.  We can easily detect this version at
compile time which is faster than configure time.

Re-add build support for the fixed-point Vorbis (Tremor) decoder, which
was dropped when switching from Autotools to Meson.

Note, that it is not possible to build both, the Vorbis and the Tremor
decoder.

Closes: #405