sb_celp: avoid division by 0

sb_celp: avoid division by 0

Co-authored by: Jean-Marc Valin jmvalin@jmvalin.ca

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/speex

Fixes https://oss-fuzz.com/testcase-detail/6065027378905088 Fixes https://issues.oss-fuzz.com/issues/389329711

changed title from arch: add EPSILON to sb_celp: avoid division by 0

changed the description

merged