[PATCH 4 of 7] templater: micro-optimize join() with empty separator

[Yuya Nishihara]

# HG changeset patch
# User Yuya Nishihara <yuya at tcha.org>
# Date 1521555388 -32400
#      Tue Mar 20 23:16:28 2018 +0900
# Node ID 2c73a43fd4dfbc6cbf1971cb192d48e74506856d
# Parent  419e9203f95ad088cea54213ddbe892beb4775bd
templater: micro-optimize join() with empty separator

diff --git a/mercurial/templateutil.py b/mercurial/templateutil.py
--- a/mercurial/templateutil.py
+++ b/mercurial/templateutil.py
@@ -558,6 +558,6 @@ def joinitems(itemiter, sep):
     for x in itemiter:
         if first:
             first = False
-        else:
+        elif sep:
             yield sep
         yield x