[MC-117722] Function if and unless always fail when executed in function

The /function command with if or unless always fails when it is executed in a function.

Create a function custom:test
```
function custom:test2 if @s
```
Create a function custom:test2
```
say test2
```
Run the function custom:test
```
/function custom:test
```
→ "test2" is not printed

Note: As workaround you can use /execute

execute @s ~ ~ ~ /function custom:test2 if @s