Problem reported by Antonio Teixeira.
* src/list.c (read_header): When POSIX says a size field must
be zero or does not represent a data count, treat it as zero.
* tests/extrac32.at: Update to match new behavior.
We now treat hard link sizes as zero even when the size fields are
nonzero, and this means the “injected” file is treated as valid
regardless of whether we list or extract.
* tests/extrac34.at: New test.
* tests/Makefile.am (TESTSUITE_AT), tests/testsuite.at: Add it.
