TOLTECS: Work around undefined subtitle behaviour at script loading

It may be because of an underlying bug, but there is at least one
case where a script is unloaded and replaced by another script while
that script slot still has an active subtitle. This causes it to
print random garbage for me, and may be causing crashes for others.

I've discussed this patch with johndoe, and he was ok with it, so
let's see how it works out.