for_each_reflog(): don't abort for bad references

If there is a file under "$GIT_DIR/logs" with no corresponding
reference, the old code was emitting an error message, aborting the
reflog iteration, and returning -1. But

* None of the callers was checking the exit value

* The callers all want to find all legitimate reflogs (sometimes for the
  purpose of determining object reachability!) and wouldn't benefit from
  a truncated iteration anyway.

So instead, emit an error message and skip the "broken" reflog, but
continue with the iteration.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

refs/files-backend.c

@@ -3324,7 +3324,7 @@ static int do_for_each_reflog(struct strbuf *name, each_ref_fn fn, void *cb_data
 				struct object_id oid;
 
 				if (read_ref_full(name->buf, 0, oid.hash, NULL))
-					retval = error("bad ref for %s", name->buf);
+					error("bad ref for %s", name->buf);
 				else
 					retval = fn(name->buf, &oid, 0, cb_data);
 			}