Check that petnames index exists

content.py

@@ -973,10 +973,13 @@ def _add_mention(base_dir: str, word_str: str, http_prefix: str,
             return True
         # try replacing petnames with mentions
         follow_ctr = 0
+        if petnames:
             for follow in following:
                 if '@' not in follow:
                     follow_ctr += 1
                     continue
+                pet = None
+                if len(petnames) > follow_ctr:
                     pet = remove_eol(petnames[follow_ctr])
                 if pet:
                     if possible_nickname != pet: