busybox

bunzip2: fix runCnt overflow from bug 10431

This particular corrupted file can be dealth with by using "unsigned".
If there will be cases where it genuinely overflows, there is a disabled
code to deal with that too.

function                                             old     new   delta
get_next_block                                      1678    1667     -11

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>