Fixed race condition in color bucket pooling
Fixed race condition in color bucket pooling

When multiple images are quantized in parallel, a thread could reduce the target bucket size before the other thread makes a bucket.

Sequence:

T1: L18-26, c=100, p.maxCap=100
T2: L18-26, c=50, p.maxCap=99
T1: L27-29, c=100, p.maxCap=99, ppanic: runtime error: slice bounds out of range [:100] with capacity 99

ericpauley/go-quantize