Fixed a bug when using an empty name in SetAddressHeader

Fixes #54

message.go

@@ -127,6 +127,10 @@ func (m *Message) SetAddressHeader(field, address, name string) {
 
 // FormatAddress formats an address and a name as a valid RFC 5322 address.
 func (m *Message) FormatAddress(address, name string) string {
+	if name == "" {
+		return address
+	}
+
 	enc := m.encodeString(name)
 	if enc == name {
 		m.buf.WriteByte('"')

message_test.go

@@ -531,6 +531,18 @@ func TestBase64LineLength(t *testing.T) {
 	testMessage(t, m, 0, want)
 }
 
+func TestEmptyName(t *testing.T) {
+	m := NewMessage()
+	m.SetAddressHeader("From", "from@example.com", "")
+
+	want := &message{
+		from:    "from@example.com",
+		content: "From: from@example.com\r\n",
+	}
+
+	testMessage(t, m, 0, want)
+}
+
 func TestEmptyHeader(t *testing.T) {
 	m := NewMessage()
 	m.SetHeaders(map[string][]string{