Resolve "USAN error in swb_tbe_enc.c: "-inf is outside the range of representable values of type 'short'" for OMASA encoding"

• Related issues: #971 (closed)
• Requested reviewers: @suhua

Reason why this change is needed

To solve the following UBSAN error:

lib_enc/swb_tbe_enc.c:2741:15: runtime error: -inf is outside the range of representable values of type 'short'
SUMMARY: UndefinedBehaviorSanitizer: float-cast-overflow lib_enc/swb_tbe_enc.c:2741:15 in 

Description of the change

Prevent ratio to be always higher than 1.0. This avoids log2(0.0) = -Inf in the following statement

idxGain = (int16_t) ( log2_f( (float) ratio ) + 0.5f );

Affected operating points

BE modification. Affects all opearting points using FB TBE inside the core coder (SCE, ISMs, OMASA, OSBA). Affects EVS as well!