Hello,

The attached patch fixes the following bug:

 * Have a scheduled item that has also has a deadline with a cusom
   prewarning cookie, e.g. <... -3d>.
 * Set `org-agenda-skip-deadline-prewarning-if-scheduled' to 7

Then in the agenda, the item is shown already 7 days before the
deadline (instead of 3). Judging from their name and documentation, the
"skip" variables `org-agenda-skip-deadline-prewarning-if-scheduled' and
`org-agenda-skip-scheduled-delay-if-deadline` should only ever skip
items in the agenda. In other words, they should only shorten the
prewarning or delay period, but never extend it. 

Best,
Tim