markused: fix option array element (fix #23089) (#25179)

vlib/v/markused/walker.v

@@ -432,6 +432,9 @@ fn (mut w Walker) expr(node_ ast.Expr) {
 			if !w.uses_array && !w.is_direct_array_access {
 				w.uses_array = true
 			}
+			if node.elem_type.has_flag(.option) {
+				w.used_option++
+			}
 		}
 		ast.Assoc {
 			w.exprs(node.exprs)

vlib/v/tests/skip_unused/option_array_init.vv

@@ -0,0 +1,6 @@
+fn main() {
+	mut a := []?u32{len: 0xFF}
+	if c := a[0] {
+		println('c:  ${c} not none!')
+	}
+}