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.

mercurial/templater.py

@@ -649,7 +649,7 b' def word(context, mapping, args):'
         splitter = None
 
     tokens = text.split(splitter)
-    if num >= len(tokens):
+    if num >= len(tokens) or num < -len(tokens):
         return ''
     else:
         return tokens[num]

tests/test-command-template.t

@@ -3368,6 +3368,11 b' Test word for invalid numbers'
   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