Don't show bogus last-checked times

Dependencies

• [2] JY7BXXOP Split viewing and editing a project
• [3] MCCHPWHE Indicate disabled/hidden projects/jobsets in the overviews
• [4] 3PNG7NIB Remove trailing whitespace
• [5] BIVZGPUT Optimise clickable rows
• [*] 7YBYT2LQ

Change contents

• replacement in src/root/project.tt at line 46
  [2.4238]→[2.4238:4320](∅→∅)
  − <td>[% INCLUDE renderDateTime timestamp = j.lastcheckedtime %]</td>
  [2.4238]

  [2.4320]
  + <td>[% IF j.lastcheckedtime; INCLUDE renderDateTime timestamp = j.lastcheckedtime; ELSE; "-"; END %]</td>