This combination would assume different block sizes throughout the code so its
better to error out.

Fixes: signed integer overflow: -1082385168 * 2 cannot be represented in type 'int'
Fixes: 19110/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_ACELP_KELVIN_fuzzer-5643993950191616
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>