encoder crash caused by ac06a15326df with --tune fast-decode

[Former user]

exists at latest tip: 07c85baedb16

command: big_buck_bunny_360p24.y4m --preset medium --bitrate 400 --vbv-bufsize 600 --vbv-maxrate 600 --aud --hrd --tune fast-decode --no-info --hash=1 --psnr --ssim --no-progress

[Deepthi Nandakumar]

This has been fixed with cadfa44f3913.