User errors in code supplied by url parameter broke error msging

[lionleaf]

This fix allows the errors to behave similar to the case where code is supplied via messages.

The purpose of this is for the dweet not to crash, but rather send iframe messages with the error which can then be displayed to the user

When opening your Pull Request, we encourage you to do the following (you can add an X to check each task):

Required to make https://github.com/dwitter-net/dwitter-frontend/pull/92 work

• [x] Run make lint to ensure that all the files are formatted and using best practices.
• [x] Link to any issues this PR is solving.

[lionleaf]

Tested on old frontend and errors still work as expected there