RDP: fix krdc crash problem when failed to connect

Don't have to call connectionError() when received the connection
failed message, for we connect the finished() signal and call
connectionClosed() when the connection is closed.
If we call connectionError() again, the krdc crashes.

connect(m_process, SIGNAL(finished(int, QProcess::ExitStatus)), SLOT(connectionClosed()));

Signed-off-by: AceLan Kao <acelan@acelan.idv.tw>