Comparison threshold definition in read_coherence_hr to align with BASOP

(Generic issue template)

Starting from a comparison with 0 in BASOP, for which it was hard to reach a sufficient precision, the comparison with 0 is transformed into comparison with a threshold to ensure same precision is used in both float and fixed point versions. The function involved is read_surround_coherence_hr() in MASA for 384kbps and 512kbps.