[non BE]: fix for issue 862 : UBSAN issue in SPAR decoder with BR switching and PLC
- Related issues:
 - Requested reviewers:
 
Reason why this change is needed
- To fix the UBSAN issue in SPAR decoder with BR switching and PLC
 
Description of the change
- Mapping of SPAR indices in time differential coding is only done if previous frame is not a bad frame.
 - Core coder's prev_bfi value is restored during bitrate switching
 
Affected operating points
- Potentially all operating points that are using prev_bfi variable from core coder.
 - For bitstream compatibility, the following levels are helpful for describing encoder
- Produced bitstream is BE compared to previous state and backward compatible. Decoded output may be non-BE when both bitrate switching and PLC is being tested.
 
 
Related to #862 (closed)