Don't include the JSON similarity percentage if it is 0.0%.

diffoscope/comparators/json.py

@@ -85,9 +85,9 @@ class JSONFile(File):
         except Exception:
             return
 
-        difference.add_comment(
-            "Similarity: {}%".format(jsondiff.similarity(a, b))
-        )
+        similarity = jsondiff.similarity(a, b)
+        if similarity:
+            difference.add_comment("Similarity: {}%".format(similarity))
 
         difference.add_comment(
             "Differences: {}".format(