cgen: fix indexexpr with orexpr (fix #21591) (#21592)

vlib/v/gen/c/index.v

@@ -324,7 +324,7 @@ fn (mut g Gen) index_of_array(node ast.IndexExpr, sym ast.TypeSymbol) {
 			if !node.is_option {
 				g.or_block(tmp_opt, node.or_expr, elem_type)
 			}
-			g.write('\n${cur_line}*(${elem_type_str}*)${tmp_opt}.data')
+			g.write('\n${cur_line}(*(${elem_type_str}*)${tmp_opt}.data)')
 		}
 	}
 }

vlib/v/tests/indexexpr_or_test.v

@@ -0,0 +1,14 @@
+struct Element {
+	children []int
+}
+
+fn f() []Element {
+	return [Element{
+		children: [1, 2, 3]
+	}]
+}
+
+fn test_main() {
+	a := f()[0]!.children[0]!.str()
+	assert dump(a) == '1'
+}