net/mail: ensure there is at least one header

Author: 0xc0d

src/net/mail/message.go

@@ -54,7 +54,10 @@ func ReadMessage(r io.Reader) (msg *Message, err error) {
 	tp := textproto.NewReader(bufio.NewReader(r))
 
 	hdr, err := tp.ReadMIMEHeader()
-	if err != nil && err != io.EOF {
+	if err == io.EOF && len(hdr) == 0 {
+		return nil, err
+	}
+	if err != nil {
 		return nil, err
 	}