This patch fixes a bug with mstsc connecting to a RDP security only FreeRDP server.
It seems like the mstsc shipped with Windows Seven considers packets after the nego_failure
packet as an error. So after trying to do TLS, depending on the timing, mstsc can print an
error message instead of retrying to connect with RDP security. With this patch, we
don't send the MCS disconnect message when the negociation has failed.
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