Prevent -0.0 from being a confidence value.

earwigbot/wiki/copyvios/workers.py

@@ -290,7 +290,7 @@ class CopyvioWorkspace(object):
 
         d_size = float(delta.size)
         return max(conf_with_article_and_delta(self._article.size, d_size),
-                   conf_with_delta(d_size))
+                   conf_with_delta(d_size), 0)
 
     def _finish_early(self):
         """Finish handling links prematurely (if we've hit min_confidence)."""