isolated the folding part of the code that's common in vq.c
isolated the folding part of the code that's common in vq.c

dezelin/celt,oneman/opus-oneman,Distrotech/celt,mumble-voip/celt-0.7.0,mumble-voip/celt-0.7.0,dezelin/celt,oneman/opus-oneman,mumble-voip/celt-0.7.0,mumble-voip/celt-0.11.0,dezelin/celt,Distrotech/celt,Distrotech/celt,mumble-voip/celt-0.11.0,mumble-voip/celt-0.11.0,oneman/opus-oneman