histedit: crashing with a more useful error message on empty defaultrev Before this, `hg --config histedit.defaultrev= histedit` would crash with File "destutil.py", line 385, in desthistedit if revs: UnboundLocalError: local variable 'revs' referenced before assignment Differential Revision: https://phab.mercurial-scm.org/D5543

#require docutils gettext

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