English grammer - If you’ll

Hello,

is it possible to say

If you will go out, please buy me a magazine.

?

I really don’t understand why it should be in 0 conditional (If you go out, please buy me a magazine) which tells us something that’s always right.

I found some explanation on this site:
http://getintoenglish.com/if-and-will-grammar/
Can we look at it like it’s something that’s unceratin therefore there can be used if and will in the same sentence?


Thank you!