stream_decoder: fix integer underflow due to malformed wasted_bits

It is pretty easy for a malformed FLAC file to underflow the "bps"
variable.  In the debug build, this results in an assertion failure in
FLAC__bitreader_read_raw_uint32():

    FLAC__ASSERT(bits <= 32);

In non-debug builds, this simply makes
FLAC__bitreader_read_raw_uint32() fail because
bitreader_read_from_client_() doesn't find enough buffer space for
2**32-1 bits.  But since the failing FLAC_ASSERT() is reasonable, this
should be caught in the FLAC__bitreader_read_raw_uint32() caller.

Signed-off-by: Erik de Castro Lopo <erikd@mega-nerd.com>
Closes: https://github.com/xiph/flac/pull/13
1 file changed