Flacdec outputs 16-bit samples, so let's check if the value of the first
sample is what we expect rather than just the first byte, which may be
different from what we expect depending on the host's endianness. Fixes
the flacdec unit tests on PPC. Also fix a bunch of leaks in the unit
tests to make valgrind happy. Fixes#582420.
from a 10-buffer audiotestsrc flac, in the case of:
- a full decode
- a decode of a seek for the full file
- a decode of a seek for a small part, smaller than the first buffer
The test fails because flacdec drops the first outgoing buffer on a seek
