Fix `@period` attributes that have whitespace errors

[wlpotter]

Cf. this comment in https://github.com/srophe/caesarea/issues/325 for an example.

• [x] fix in existing data
• [x] troubleshoot to see if this is the post-processor or form that is introducing these.

[wlpotter]

Hmm I can't seem to find the error in the post-processor.