markov: fake a __stop if a k1,k2 has no v

this shouldn't have happened, but i'm guessing some previous crash put
some buggy data into my database, so let's just be careful and do this.
a k1,k2 could have had any value for v, but not knowing what else to do
in this corner case, we'll just use a stop and let the caller decide
if they want to keep going

dr_botzo/markov/lib.py

@@ -114,6 +114,10 @@ def get_or_create_target_context(target_name):
 def get_word_out_of_states(states, backwards=False):
     """Pick one random word out of the given states."""
 
+    # work around possible broken data, where a k1,k2 should have a value but doesn't
+    if len(states) == 0:
+        states = MarkovState.objects.filter(v=MarkovState._stop)
+
     new_word = ''
     running = 0
     count_sum = states.aggregate(Sum('count'))['count__sum']