Decode bytes after full line received

Wait to decode bytes received from the server until a full line has
been received. Data received from the server could end in the middle
of a UTF-8 multibyte sequence, and decoding the data without waiting
for the rest of the line would result in a decoding error.

pyrcb.py

@@ -88,7 +88,7 @@ class IRCBot(object):
     # Initializes attributes.
     def _init_attributes(self):
-        self._buffer = ""
+        self._buffer = b""
         self.socket = None
         self.hostname = None
         self.port = None
@@ -893,13 +893,14 @@ class IRCBot(object):
     # Reads a line from the socket.
     def readline(self):
-        while "\r\n" not in self._buffer:
+        while b"\r\n" not in self._buffer:
             data = self.socket.recv(1024)
             if not data:
                 return
-            self._buffer += data.decode("utf8", "ignore")
-        line, self._buffer = self._buffer.split("\r\n", 1)
+            self._buffer += data
+        line_bytes, self._buffer = self._buffer.split(b"\r\n", 1)
+        line = line_bytes.decode("utf8", "ignore")
         if self.debug_print:
             self.print_function(line)
         return line