bug#39944: 27.0.90; JIT Stealth timer errors

[Eli Zaretskii]

> Date: Fri, 06 Mar 2020 12:01:46 +0200
> From: Eli Zaretskii <eliz@gnu.org>
> 
> 
> I see these errors in the 27.0.90 pretest from time to time:
> 
>   Error running timer ‘jit-lock-stealth-fontify’: (error "Invalid time 
> format")

Additional information which is probably related: the *Message* buffer
shows this from time to time:

  run-at-time: Invalid time format
  ([nil 24162 5043 0 5 display-time-event-handler nil nil 0] [nil 24162 5046 
46875 nil undo-auto--boundary-timer nil nil 0] [nil 24162 5098 187500 60 
battery-update-handler nil nil 0] [nil 24162 54768 140625 86400 run-hooks 
(midnight-hook) nil 0])