avcodec/ffwavesynth: Simplify lcg_seek(), avoid negative case
Fixes: negation of -
9223372036854775808 cannot be represented in type 'int64_t' (aka 'long'); cast to an unsigned type to negate this value to itself
Fixes: 15289/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_FFWAVESYNTH_fuzzer-
5709034499342336
Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit
8c022099351c04ae21e0b8696ea71a690ed03cd2)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>