templater: protect word() from crashing on out of range negative value stable

templater: protect word() from crashing on out of range negative value

The function isn't documented to work with negative values at all, but it does,
which can be useful.  However, the range check didn't account for this.

--- a/mercurial/templater.py	Thu Oct 01 12:07:20 2015 -0500
+++ b/mercurial/templater.py	Mon Oct 05 12:37:26 2015 -0400
@@ -649,7 +649,7 @@
         splitter = None
 
     tokens = text.split(splitter)
-    if num >= len(tokens):
+    if num >= len(tokens) or num < -len(tokens):
         return ''
     else:
         return tokens[num]

--- a/tests/test-command-template.t	Thu Oct 01 12:07:20 2015 -0500
+++ b/tests/test-command-template.t	Mon Oct 05 12:37:26 2015 -0400
@@ -3368,6 +3368,11 @@
   hg: parse error: word expects an integer index
   [255]
 
+Test word for out of range
+
+  $ hg log -R a --template "{word(10000, desc)}"
+  $ hg log -R a --template "{word(-10000, desc)}"
+
 Test indent and not adding to empty lines
 
   $ hg log -T "-----\n{indent(desc, '>> ', ' > ')}\n" -r 0:1 -R a