If e.g. a document is slow to redraw, scrolling it by holding down a key such
as PageDown can make LO lag behind and continue processing the queued up
input events even (long) after the key has been released. Since with autorepeat
keyboard events the normal user expectations are to hold it until something
happens and the exact number of the events doesn't matter, simply discard
excessive autorepeat keyboard events if LO can't keep up with them.

Change-Id: I45acdc9aa5033647fb80760991437dddfcb6591c