fix(neptun_smart_waterleak): default multizone to on

Since the device does not always report the multizone status locally,
default to enabling zone 2 to avoid having it unavailable when it should
be available.

Issue #2260

custom_components/tuya_local/devices/neptun_smart_waterleak.yaml

@@ -128,6 +128,10 @@ entities:
         type: boolean
         name: available
         optional: true
+        mapping:
+          # Since the device does not always send this, default to available
+          - dps_val: null
+            value: true
   - entity: switch
     name: Multi zone
     icon: "mdi:select-group"