Improves error-handling in LibarchivePlugin::list().

Previously we only checked whether we could read until the end of the
archive, and even if we couldn't there was no error shown to the user.
Now we check the return value of both archive_read_next_header() and
archive_read_data_skip(), and show a corrupt archive query if either
was not successful.

This partially solves bug 411074, as Ark now at least gives a warning
when opening a corrupt archive with libarchiveplugin. We still need to
improve error-handling when extracting, but this requires some
refactoring first so will be done later.
CCBUG: 411074
Differential Revision: D29383