[vdr] Cut marks editing problem

[Olaf Titz]

I'm editing a recording with some errors in it (errors of the kind
"broken MPEG kills vdr-sxfe"). Looks like the index.vdr is broken, so
I run genindex. After that, some existing cut marks are not on a GOP
boundary any more (looks like genindex really has fixed something). I
can't edit these cut marks any more. When I put the cursor on the
broken mark, neither of 4 6 7 9 keys do anything. With 0 the mark is
not deleted, rather a new one generated at the right position but I
can't get rid of the broken mark.

Proposed fix: on the 7 and 9 keys, look if the mark is really on a GOP
boundary, and if not, scan for the next one, adjusting the mark.
This would also help with manual editing of the marks.vdr file.

Olaf