As of 2.6 the smtplib uses the ssl module, until 2.5 it uses _ssl, I
*think* that this issue would bring an Exception on 2.5 while on 2.6
would return a zero length string:
"""
def read(self, len=1024):

        """Read up to LEN bytes and return them.
        Return zero-length string on EOF."""

        return self._sslobj.read(len)
"""

wich would fulfill the "if not chr:"