phabricator: abort if phabsend gets empty revs

Previously we didn't abort. Now we abort if revs is empty. This is
consistent with "hg export" behavior. Maybe "return 1" is also a reasonable
behavior, but that's inconsistent with the existing "hg export".

contrib/phabricator.py

@@ -271,6 +271,9 b' def phabsend(ui, repo, *revs, **opts):'
     revs = list(revs) + opts.get('rev', [])
     revs = scmutil.revrange(repo, revs)
 
+    if not revs:
+        raise error.Abort(_('phabsend requires at least one changeset'))
+
     # Send patches one by one so we know their Differential Revision IDs and
     # can provide dependency relationship
     lastrevid = None