fix for reading empty vin

When VIN is empty, it contains 0x00 or 0xFF which can't be converted to ascii by decode function.

ecu.py

@@ -664,7 +664,7 @@ def getDisplayValue(self, elm_data, dataitem, ecu_endian):
             return None
 
         if self.bytesascii:
-            return bytes.fromhex(value).decode('utf-8')
+            return bytes.fromhex(value).decode('utf-8',errors="ignore")
 
         # I think we want Hex format for non scaled values
         if not self.scaled: