[NonBE] Resolve "OMASA ltv crashes for bitrate switching to TD stereo"

• Related issues: #874 (closed), #877 (closed)
• Requested reviewers:

Reason why this change is needed

The OMASA crashes with long test-vector in case of bitrate switching. Using the following command-line:

IVAS_cod -q -ism_masa 3 1 ltv48_OMASA_3ISM_1TC_ISM1.csv ltv48_OMASA_3ISM_1TC_ISM2.csv ltv48_OMASA_3ISM_1TC_ISM3.csv ltv48_OMASA_3ISM_1TC.met sw_13k2_512k_2fr_start_48k_omasatechs_3ism.bin ltv48_OMASA_3ISM_1TC.wav bit

there is a crash in frame 2392 which involves a switching from 48 kbps to 13.2kbps.

The problem comes from the fact that the previous frame at 48 kbps is coded using TD stereo which is kept also in the first 13.2 kbps frame. However, TD stereo should be avoided in MASA/OMASA at 13.2kbps.

Description of the change

• Switching from TD to DFT is enabled in the select_stereo_mode().
• Bitrate surplus is reset (was missing) when switching to lower bitrates in OMASA.

Affected operating points

• There were crashes.
  1. Produced bitstream is nonBE for OMASA where CPE uses TD.

Related to #874 (closed)