plugin: lua: fix object dtor
plugin: lua: fix object dtor

When freed from a reference cycle collection, the object dtor attempts
to access member of another object, which is not guaranteed to exist due
to reference cycles.

Signed-off-by: Yuxuan Shui <7f7e1535bcd10fa942d56a3436533af20f33203f@gmail.com>

yshui/deai,yshui/deai,yshui/deai