fix(transport-smtp): Fix transparency codec

It fails to add transparency when a period is preceded by two
successive CRLF.

src/transport/smtp/client/mod.rs

@@ -78,7 +78,15 @@ impl ClientCodec {
                     match self.escape_count {
                         0 => self.escape_count = if *byte == b'\r' { 1 } else { 0 },
                         1 => self.escape_count = if *byte == b'\n' { 2 } else { 0 },
-                        2 => self.escape_count = if *byte == b'.' { 3 } else { 0 },
+                        2 => {
+                            self.escape_count = if *byte == b'.' {
+                                3
+                            } else if *byte == b'\r' {
+                                1
+                            } else {
+                                0
+                            }
+                        }
                         _ => unreachable!(),
                     }
                     if self.escape_count == 3 {
@@ -111,6 +119,7 @@ mod test {
         let mut buf: Vec<u8> = vec![];
 
         codec.encode(b"test\r\n", &mut buf);
+        codec.encode(b"test\r\n\r\n", &mut buf);
         codec.encode(b".\r\n", &mut buf);
         codec.encode(b"\r\ntest", &mut buf);
         codec.encode(b"te\r\n.\r\nst", &mut buf);
@@ -121,7 +130,7 @@ mod test {
         codec.encode(b"test", &mut buf);
         assert_eq!(
             String::from_utf8(buf).unwrap(),
-            "test\r\n..\r\n\r\ntestte\r\n..\r\nsttesttest.test\n.test\ntest"
+            "test\r\ntest\r\n\r\n..\r\n\r\ntestte\r\n..\r\nsttesttest.test\n.test\ntest"
         );
     }