nvl hide transition doesn't work in some cases

[Elckarow]

following #5426 and is what i believe #5362 was trying to fix

define config.adv_nvl_transition = dissolve
define config.nvl_adv_transition = dissolve

say you have this

some_adv_character "talking"

show bg 1

some_nvl_character "talking"

it works as expected. the adv textbox fades out while bg 1 and the nvl textbox fade in

but if you do the opposite

some_nvl_character "talking"

show bg 1

some_adv_character "talking"

bg 1 appears instantly