core dumped when turn on Multithreading switch

[chuanflow]

I add

#define BRUNSLI_EXPERIMENTAL_GROUPS 1

in c/tools/cbrunsli.cc

then try to compress a jpg, but a core dumped. The jpg picture is in the attachment.

c/enc/write_bits.cc:26 (~Storage)
Aborted (core dumped)

[chuanflow]

it seems that DC part_size is not enough when components equal 1.
serialize kBrunsliDCDataTag

size_t part_size = 128 * (128 + 16) * jpg.components.size();
part.resize(part_size);

[eustas]

Will take a look soon.