Fixes stv crash issue due to log(0) computation in sub function of ApplyFdCng_fx()

[x] The crash occurs due to computation of log(0) by
BASOP_Util_Log2, which was not handled in the EVS
implemented scalebands().
[x] Created a separate copy of scalebands() as
scalebands_fx() for IVAS path because after making
the change in EVS function, many streams got
bit-inexact in decoder and encoder for EVS bit-exact
testing.