datatypes: fix linked list of map (fix #17570) (#17573)

vlib/datatypes/linked_list.v

@@ -207,7 +207,7 @@ pub fn (mut iter ListIter[T]) next() ?T {
 	if iter.node == unsafe { nil } {
 		return none
 	}
-	res := iter.node.data
+	res := unsafe { iter.node.data }
 	iter.node = iter.node.next
 	return res
 }

vlib/datatypes/linked_list_test.v

@@ -168,3 +168,26 @@ fn test_linked_list_separate_iterators() {
 	}
 	assert res == [1, 2, 3]
 }
+
+struct Foo {
+mut:
+	field LinkedList[map[string]int]
+}
+
+fn test_linked_list_map() {
+	mut foo := Foo{}
+	foo.field.push({
+		'one': 1
+	})
+	foo.field.push({
+		'two': 2
+	})
+	println(foo)
+	mut iter := foo.field.iterator()
+	assert iter.next()! == {
+		'one': 1
+	}
+	assert iter.next()! == {
+		'two': 2
+	}
+}