RTC: Allow username is optinal
RTC: Allow username is optinal

ossrs/srs,winlinvip/srs,winlinvip/srs,ossrs/srs,winlinvip/srs,ossrs/srs,ossrs/srs,ossrs/srs,winlinvip/srs,ossrs/srs,winlinvip/simple-rtmp-server,winlinvip/srs,winlinvip/srs