USAN null pointer in MASA external renderer to Ambisonics
### Basic info
- Commit SHA: c61f50dd
### Bug description
MR !1215 for enabling MASA external renderer tests fails in pipeline [183021](https://forge.3gpp.org/rep/ivas-codec-pc/ivas-codec/-/jobs/183021) for rendering to Ambisonics with a USAN null-pointer error:
```
usan_log_test_masa[20ms-MASA1-FOA].18497:SUMMARY: UndefinedBehaviorSanitizer: nullptr-with-nonzero-offset /builds/rep/ivas-codec-pc/ivas-codec/lib_rend/ivas_dirac_rend.c:2144:56
```
Command:
```
/builds/rep/ivas-codec-pc/ivas-codec/IVAS_rend -i /builds/rep/ivas-codec-pc/ivas-codec/tests/renderer/data/spectral_test_8ch_48kHz.wav -if 7_1 -o /builds/rep/ivas-codec-pc/ivas-codec/tests/renderer/cut/7_1_to_BINAURAL_ROOM_REVERBNoneNone.wav -of BINAURAL_ROOM_REVERB -fs 48 -no_delay_cmp -q
```
<!--- Copy test job URL here -->
Link to test pipeline: [183021](https://forge.3gpp.org/rep/ivas-codec-pc/ivas-codec/-/jobs/183021)
This seems to be related to #879 in internal renderer solved in MR !1186.
issue