hgk: Don't choke on empty changelogs

hgext/hgk.py

@@ -131,7 +131,7 b' def catcommit(repo, n, prefix, changes=N'
     date_ar = changes[2]
     date = int(float(date_ar[0]))
     lines = changes[4].splitlines()
-    if lines[-1].startswith('committer:'):
+    if lines and lines[-1].startswith('committer:'):
         committer = lines[-1].split(': ')[1].rstrip()
     else:
         committer = changes[1]