Implement improved guarding as suggested

Author: bouwew

plugwise_usb/nodes/circle.py

@@ -532,10 +532,10 @@ async def _energy_log_records_load_from_cache(self) -> bool:
             )
             return False
         restored_logs: dict[int, list[int]] = {}
-        log_data = cache_data.split("|")
-        if len(log_data) == 0:
+        if cache_data == "":
             return False
 
+        log_data = cache_data.split("|")
         for log_record in log_data:
             log_fields = log_record.split(":")
             if len(log_fields) == 4: