Previously, only the extra fields stored in the central directory were
being read in. In reality it is often the case that the extra field in
the central directory is just a marker, and the full data is in the
local header. So we need to read both in and merge the two into the
final correct extra field. This merging infrastructure was already
implemented in the extra field code but we never actually read the
local extra fields in until now.
Reading the central directory headers and local entry headers seems
rather fragile, so we can't just read one over the other and hope to end
up with a correctly merged set of extra fields because this breaks other
things. So we need to specifically read the local extra field data and
merge just those bits.
This commit also fixes a couple of tests that were 'broken' by us now
reading extra fields in correctly!