cgen: fix nested map index check (fix #14683) (#14687)

vlib/v/gen/c/index.v

@@ -484,7 +484,7 @@ fn (mut g Gen) index_of_map(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/nested_map_index_test.v

@@ -0,0 +1,24 @@
+struct Foo {
+mut:
+	foo map[int]Bar
+}
+
+struct Bar {
+mut:
+	bar map[int]string
+}
+
+fn test_nested_map_index() ? {
+	f := Foo{
+		foo: {
+			11: Bar{
+				bar: {
+					22: 'hello'
+				}
+			}
+		}
+	}
+	ret := f.foo[11]?.bar[22]?
+	println(ret)
+	assert ret == 'hello'
+}