Encoder crash for Stereo at 48/64kbps DTX on/off in kernel_switch_trafo_fx()
# Basic info
<!--- Add commit SHA used to reproduce -->
- Float reference:
- Encoder (float):
- Decoder (float):
- Fixed point:
- Encoder (fixed): 909f10c34d1ccab42ecc9aa598ee06671cc101fd
- Decoder (fixed):
# Bug description
The fixed point encoder crashes with an assert:
```
Frames processed: 1535 Assertion failed: (0), function L_add, file basop32.c, line 1784.
```



# Ways to reproduce
Box folder: ...\Box_EXTERNAL_IVAS_BASOP_VERIFICATION\issues\issue-1157
<!-- Commandline or script -->
```bash
./IVAS_cod_fx -stereo -max_band FB 48000 48 stereo-noisy_speech-p800-2-cat4-lab_b-20ms_aligned_files_concatenated_48.10dB.wav bit
./IVAS_cod_fx -stereo -max_band FB 64000 48 stereo-noisy_speech-p800-2-cat4-lab_b-20ms_aligned_files_concatenated_48.10dB.wav bit
./IVAS_cod_fx -dtx -stereo -max_band FB 48000 48 stereo-noisy_speech-p800-2-cat4-lab_b-20ms_aligned_files_concatenated_48.10dB.wav bit
./IVAS_cod_fx -dtx -stereo -max_band FB 64000 48 stereo-noisy_speech-p800-2-cat4-lab_b-20ms_aligned_files_concatenated_48.10dB.wav bit
```
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issue