Fix use-after-free for internal scrollbar after ListBox::Clear
Fix use-after-free for internal scrollbar after ListBox::Clear

Clear() deletes the internal scrollbar, which still has a refernce (and
is used in update and render calls) causing crashes/weird stuff in the
ufopaedia group.

Instead, reconstruct the internal scrollbar is needed after it's deleted
in Clear() (kinda excessive but seems to work)

ShadowDancer/OpenApoc,AndO3131/OpenApoc,FranciscoDA/OpenApoc,FranciscoDA/OpenApoc,Istrebitel/OpenApoc,steveschnepp/OpenApoc,pmprog/OpenApoc,FranciscoDA/OpenApoc,AndO3131/OpenApoc,pmprog/OpenApoc,ShadowDancer/OpenApoc,AndO3131/OpenApoc,Istrebitel/OpenApoc,steveschnepp/OpenApoc