ui: guess WAS URL from interface IP if WAS_IP is unset

ui.py

@@ -93,7 +93,10 @@
     was_url = ""
     if len(user_nvs) == 0:
         try:
-            was_url = f"ws://{environ['WAS_IP']}:8502/ws"
+            if environ.get('WAS_IP') is not None:
+                was_url = f"ws://{environ['WAS_IP']}:8502/ws"
+            else:
+                was_url = f"ws://{get_ip()}:8502/ws"
             st.info("We tried to guess your WAS URL. Please make sure your Willow devices can reach this URL!")
         except Exception:
             st.info("We couldn't guess your WAS URL. Please make sure your Willow devices can reach the URL you enter!")