extract a function for `generate-html`
Fix issue with whitespace
Change the exception handling like so:
- If the plugin catches an exception:
  - if the exception has an `:exit-code`, then
    - generate the HTML results if configured to do so
    - and rethrow the exception to result in a build failure
  - if the exception does not have an `:exit-code`, then
    - print a message containing the exception
    - discard the exception
- Generate the HTML report
  - this occurs if:
    - there was no exception thrown, or
    - the exception was discarded
Remove an unnecessary nil check