urllib: fixed regression in the set function (#13455)

vlib/net/urllib/values_test.v

@@ -0,0 +1,38 @@
+// Copyright (c) 2019-2022 Alexander Medvednikov. All rights reserved.
+// Use of this source code is governed by an MIT license
+// that can be found in the LICENSE file.
+module urllib
+
+fn test_add_key_val() {
+	mut values := Values{}
+	values.add('key', 'value')
+	val := values.get('key')
+	assert val == 'value'
+}
+
+fn test_get_all_with_key() {
+	mut values := Values{}
+	values.add('key', 'value1')
+	values.add('key', 'value2')
+	key_values := values.get_all('key')
+	assert key_values == ['value1', 'value2']
+}
+
+fn test_set_with_key() {
+	mut values := Values{}
+	values.add('key', 'value1')
+	values.add('key', 'value2')
+	values.add('key1', 'value2')
+	values.set('key1', 'vlang')
+	key_values := values.get_all('key')
+	key2_values := values.get_all('key1')
+	assert key_values == ['value1', 'value2']
+	assert key2_values == ['vlang']
+}
+
+fn test_set_missing_key() {
+	mut values := Values{}
+	values.set('err', 'err1')
+	vals := values.get_all('err')
+	assert vals == ['err1']
+}