tap: fix exit status when we have exactly 256 errors.
[ccan] / ccan / tap /
drwxr-xr-x   ..
-rw-r--r-- 1486 _info
-rw-r--r-- 9855 tap.3
-rw-r--r-- 9251 tap.c
-rw-r--r-- 8309 tap.h
drwxr-xr-x - test