[O] Custom timestamps in date ranges

[jeeger]

Hello!

I have a single-line patch to contribute. In my org-mode version (Org 
mode version 9.0.9 (9.0.9-30-g796a78-elpa)), custom timestamps do not 
correctly apply to date ranges. Only the second date is replaced in the 
custom date format. I've tracked this down to org-activate-dates. The 
line

      (if (match-end 3)
                  (org-display-custom-time (match-beginning 3) (match-end 3))
                  (org-display-custom-time (match-beginning 1) (match-end 1)))

leads to only the second of the date range being fontified. The 
corrected version is:

        (when (match-end 3)
                (org-display-custom-time (match-beginning 3) (match-end 3)))
        (org-display-custom-time (match-beginning 1) (match-end 1))

This fontifies the first date correctly as well.

Regards,
Jan Seeger