Properly cleanup mutex on failure.
    
    If the call to create socket fails we leave a dangling lock and the client
    enters into a deadlock on the next call.
    
    Fixes: https://fedorahosted.org/gss-proxy/ticket/121
    
    Signed-off-by: Simo Sorce <simo@redhat.com>
    Reviewed-by: Günther Deschner <gdeschner@redhat.com>