Fix GcAdpcm encoder overflow bug
Fix GcAdpcm encoder overflow bug

It almost never happens, but if the difference between the predicted sample and actual sample is more than the square root of INT_MAX, the squared distance will overflow and become negative, causing the encoder to choose the wrong coefficients for that ADPCM frame.

Thealexbarney/LibDspAdpcm,Thealexbarney/LibDspAdpcm,Thealexbarney/VGAudio,Thealexbarney/VGAudio