Not reading dsn config at compile time

[Sgoettschkes]

This PR attempts to fix #440.

As described in the bug report, the :dsn config value got read at compile time, failing if something else then a value that can be parsed by URI.parse/1 is present.

I added a test as well but I'm not 100% happy as it does not confirm that Sentry.config.dsn/0 is not called at compile time but rather that a call to root_source_code_paths does not evaluate the dsn config variable. Calling get_config without the check_dsn: false option at compile time somewhere else will result in the same error and is not catched by my test. I'm currently not sure on how to test this.

[mitchellhenke]

Thank you so much for catching this and sending a fix!

I will look further into the case you mentioned, but I think releasing this fix is more urgent 🙂

[Sgoettschkes]

Thanks for the fast response! I'm glad I could contribute back!