Cache configuration checks should consider negative values for NumCounters/MaxCost/BufferItems

[ankon]

Found while reading through the code:

ristretto/cache.go

Lines 169 to 174 in c67e079

	case config.NumCounters == 0:
	return nil, errors.New("NumCounters can't be zero")
	case config.MaxCost == 0:
	return nil, errors.New("MaxCost can't be zero")
	case config.BufferItems == 0:
	return nil, errors.New("BufferItems can't be zero")

The checks are fine, but given that these are int64s they could be <0 which the checks won't catch unless I'm missing something.