Make clear to user that there is no content available when text is changed in the sidebar and a 404 occurs (i.e. the selected text is not available for this milestone)
Per #121:
Show empty text on 404 selected from sidebar
During data generation, don't write empty text to HTML when content unavailable, instead allow 404s to occur and be handled by the above
Reduce overall API requests, as the API was getting pinged for every page even before selectedTimestamp had loaded and it was still undefined
In this PR
selectedTimestamp
had loaded and it was still undefined