cgen: fix assigning option of array index (fix #23451)

[yuyi98]

This PR fix assigning option of array index (fix #23451).

• Fix assigning option of array index.
• Add test.

fn make_option() ?string {
	return none
}

fn main() {
	arr := [make_option()]
	unwrapped := arr[99] or { 'unknown' } // <- out of bounds access!
	println('... ${unwrapped}')
}

PS D:\Test\v\tt1> v run .
... Option('unknown')

[huly-for-github]

Connected to Huly®: V_0.6-21885

[spytheman]

Excellent work.