wireproto: do not abort after successful lookup

wireproto: do not abort after successful lookup

As far as I can tell, this interface originally used 'return' here, so the
"fallthrough" to self._abort made sense. When it was switched to 'yield' this
didn't make sense, but doesn't impact most uses because the 'plain' wrapper in
peer.py's 'batchable' decorator only attempts to yield two items (args and
value).

When using iterbatch, however, it attempts to verify that the @batchable
generators only emit 2 results, by expecting a StopIteration when attempting to
access a third.

Differential Revision: https://phab.mercurial-scm.org/D608

--- a/mercurial/wireproto.py	Fri Sep 01 16:44:30 2017 -0700
+++ b/mercurial/wireproto.py	Fri Sep 01 14:00:13 2017 -0700
@@ -235,7 +235,8 @@
         success, data = d[:-1].split(" ", 1)
         if int(success):
             yield bin(data)
-        self._abort(error.RepoError(data))
+        else:
+            self._abort(error.RepoError(data))
 
     @batchable
     def heads(self):