Enable stereo cng div by zero fix

[x] Changes pulled in from ivas-codec-pc/ivas-codec!1431 (merged) are enabled. The code was already included but was disabled until these were included in ivas-float-update.

EVS 26.444 BE test passes.
pytests results: 597 failed, 381 skipped

MLD scores:
Original inputs:
MLD > 10: 80
MLD > 5 : 140
MLD < 5 : 377

+10dB inputs:
MLD > 10: 214
MLD > 5 : 189
MLD < 5 : 193

-10dB inputs:
MLD > 10: 28
MLD > 5 : 97
MLD < 5 : 472