Allow plugin inline displays to shrink

Allow plugin inline displays to shrink

Plugin inline displays were forbidden to shrink as this might cause a deadlock
when the shrinkage causes the scrollbar to disappear.

display shrink → scrollbar unneeded → scrollbar disappears →
more horizontal space -> display grows -> scrollbar appears →
less horizontal space -> display shrink and so forth

This was formerly avoided by not allowing display shrinkage.

The solution proposed here sets the maximum height of the display to the
current height, if a scrollbar is present during resizing and has not been
present during the last resizing. So if this scrollbar disappears (after
resizing it might no longer be needed), the display would have the possibility
to grow, but it does not grow vertically as the maximum height is limited to
the current height.