No speex samples with non default frame sizes are known (to me)
the official speexenc seems to only generate the 3 default ones.
Thus it may be that the fuzzer samples where the first non default
values encountered by the decoder.
Possibly the "<" should be "!="

Fixes: out of array access
Fixes: 42821/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_SPEEX_fuzzer-5640695772217344

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpegSigned-off-by: Michael Niedermayer <michael@niedermayer.cc>