diff -r 51f10e6d66c7 -r e2697acd9381 mercurial/templatefilters.py
--- a/mercurial/templatefilters.py	Tue Oct 02 12:43:54 2018 -0700
+++ b/mercurial/templatefilters.py	Wed Oct 03 10:27:44 2018 -0700
@@ -200,7 +200,7 @@
             if not m:
                 uctext = encoding.unifromlocal(text[start:])
                 w = len(uctext)
-                while 0 < w and uctext[w - 1].isspace():
+                while w > 0 and uctext[w - 1].isspace():
                     w -= 1
                 yield (encoding.unitolocal(uctext[:w]),
                        encoding.unitolocal(uctext[w:]))