tests/test-gendoc-sv.t

phab-refresh: do not error out when the stack is empty

Actually, empty stack is easier to get than I expected (and harmless). When a
stack is publish, heptapod will detect the even, empty the stack (triggering CI)
and "forgetting" the branch afterward.

So we stop returning as error in this case.

Differential Revision: https://phab.mercurial-scm.org/D9513

#require docutils gettext

  $ $TESTDIR/check-gendoc sv
  checking for parse errors