FXSetBlendVariableScript Fix 1.0.0

What is this.

the original script can cause save bloat up to ctd on load. 

(After doing this  bring the lexicon back quest I realised a save bloat with active scripts.)

Changed the original script, replaced while loop with registerforsingleupdate() and change onunload() event into the more reliable oncelldetach() 

No more active script bloat in save.