If an index entry for a file that is not in HEAD is in conflicted state,
when diffing HEAD with the index, the status field of the corresponding git_diff_delta was incorrectly reported as GIT_DELTA_ADDED instead of GIT_DELTA_CONFLICTED.

This was due to handle_unmatched_new_item() initially setting the status
to GIT_DELTA_CONFLICTED but then overriding it later with GIT_DELTA_ADDED.