Fixes problems with unstable filter detection
Fixes problems with unstable filter detection

LPC_inverse_pred_gain_QA() was failing to detect unstable filters
because of insufficient numerical precision. Precision was increased
to Q24 for LPC coefs and the reciprocal now uses all the precision
available (variable shift right from the start).

oneman/opus-oneman,oneman/opus-oneman,oneman/opus-oneman