Fill in 0.5 for undefined ratio.

When there are no calls and no smses (of a particular type), the ratio is undefined. But since their number is the same, I argue that the ratio can represent that with a 0.5, similarly to the case where no_calls_all = no_sms_all != 0.

features/communication.py

@@ -337,5 +337,6 @@ def calls_sms_features(
             )
             # Calculate new features and create additional columns
         )
+        .fillna(0.5, downcast="infer")
     )
     return count_joined