bug #96536: rmlabelinfo() of tape/initlabel.c corrupts memory if called more than once

The castor::tape::tapebridge::BridgeProtocolEngine::rtcpTapeErrReqRtcpdCallback()
method currently hinders the shutdown of rtcpd in error conditions by
acknowledging an rtcpd RTCP_TAPEERR_REQ with the acknowledge of an
RTCP_TAPE_REQ message.  Rtcpd detects a protocol error which confuses the
shutdown sequence.

This commit correctly the acknowledge message send by the tapebridged daemon.