Crash in ISM DTX

Some ISM DTX modes crash in the encoder when using the ltv testvectors from the ivas-pc-testfiles repo:

Encoding failed for /home/gitlab-runner/builds/rZGLsUF2/0/rep/ivas-codec-pc/ivas-codec/out/enc/ltv48_1ISM_ISM1_b48_dtx_fb_cbr.192
Encoding failed for /home/gitlab-runner/builds/rZGLsUF2/0/rep/ivas-codec-pc/ivas-codec/out/enc/ltv48_1ISM_ISM1_b48_dtx_swb_cbr.192
Encoding failed for /home/gitlab-runner/builds/rZGLsUF2/0/rep/ivas-codec-pc/ivas-codec/out/enc/ltv48_2ISM_ISM2_b96_dtx_swb_cbr.192
Encoding failed for /home/gitlab-runner/builds/rZGLsUF2/0/rep/ivas-codec-pc/ivas-codec/out/enc/ltv48_2ISM_ISM2_b96_dtx_fb_cbr.192
Encoding failed for /home/gitlab-runner/builds/rZGLsUF2/0/rep/ivas-codec-pc/ivas-codec/out/enc/ltv48_4ISM_ISM4_b192_dtx_swb_cbr.192
Encoding failed for /home/gitlab-runner/builds/rZGLsUF2/0/rep/ivas-codec-pc/ivas-codec/out/enc/ltv48_4ISM_ISM4_b192_dtx_fb_cbr.192
Encoding failed for /home/gitlab-runner/builds/rZGLsUF2/0/rep/ivas-codec-pc/ivas-codec/out/enc/ltv48_1ISM_ISM+1_b48_dtx_swb_cbr.192
Encoding failed for /home/gitlab-runner/builds/rZGLsUF2/0/rep/ivas-codec-pc/ivas-codec/out/enc/ltv48_1ISM_ISM+1_b48_dtx_fb_cbr.192
Encoding failed for /home/gitlab-runner/builds/rZGLsUF2/0/rep/ivas-codec-pc/ivas-codec/out/enc/ltv48_2ISM_ISM+2_b96_dtx_swb_cbr.192
Encoding failed for /home/gitlab-runner/builds/rZGLsUF2/0/rep/ivas-codec-pc/ivas-codec/out/enc/ltv48_2ISM_ISM+2_b96_dtx_fb_cbr.192
Encoding failed for /home/gitlab-runner/builds/rZGLsUF2/0/rep/ivas-codec-pc/ivas-codec/out/enc/ltv48_4ISM_ISM+4_b192_dtx_swb_cbr.192
Encoding failed for /home/gitlab-runner/builds/rZGLsUF2/0/rep/ivas-codec-pc/ivas-codec/out/enc/ltv48_4ISM_ISM+4_b192_dtx_fb_cbr.192

This does seem to only be happening in FB and SWB, WB runs through.

Reproduce with e.g.:

IVAS_cod -ism 1 NULL -dtx -max_band swb 48000 48 ivas-pc-testfiles/ltv48_1ISM.wav bit

I tried on the branch for !747 (merged) as there was another crash in ISM addressed already, but the crash also happens there.