OSBA bitrate switching crashes with MONO output

OSBA bitrate switching modes return segmentation fault when output configuration is MONO. This is not caused by #752 (closed) and issue was still there before.

Example to reproduce:

IVAS_cod -ism_sba 2 3 scripts/testv/stvISM1.csv scripts/testv/stvISM2.csv -max_band fb scripts/switchPaths/sw_13k2_512k.bin 48 scripts/testv/stvOSBA_2ISM_3OA48c.wav bit