Perform unique checks for InvenTreeModelSerializer in DRF

- Prevents ValidationError from throwing in the wrong spot and not being handled

InvenTree/InvenTree/serializers.py

@@ -50,6 +50,7 @@ class InvenTreeModelSerializer(serializers.ModelSerializer):
 
         # Now ensure the underlying model is correct
         instance = self.Meta.model(**data)
+        instance.validate_unique()
         instance.clean()
 
         return data