list-objects.c: don't segfault for missing cmdline objects
When a command is invoked with both --exclude-promisor-objects,
--objects-edge-aggressive, and a missing object on the command line,
the rev_info.cmdline array could get a NULL pointer for the value of
an 'item' field. Prevent dereferencing of a NULL pointer in that
situation.
Properly handle --ignore-missing. If it is not passed, die when an
object is missing. Otherwise, just silently ignore it.
Signed-off-by: Matthew DeVore <matvore@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>