[z1862] Fix script command modify_npc_flag

Thanks to faq for pointing.
I checked both udb and ytdb, and they don't use this command yet;
If however you use it already check your scripts. (The toggle/add/remove flag must be set in `data_flags`) Sorry for the inconvenience.
Alos added a forgotten break.

Signed-off-by: Schmoozerd <schmoozerd@scriptdev2.com>

(based on commit 4dbc136)

(based on commit [s1424] - 41535ac)