Decline VNC approval early when no console user is logged in

client/vnc/server/console_user_windows.go

@@ -0,0 +1,13 @@
+package server
+
+// consoleHasInteractiveUser returns true when there is a logged-in user
+// session on the box. At the lock/login screen WTSQueryUserName is empty,
+// which means there is nobody to display an approval prompt to. Callers
+// should decline without waiting on the broker in that case.
+func consoleHasInteractiveUser() bool {
+	sid := getActiveSessionID()
+	if sid == 0 {
+		return false
+	}
+	return wtsSessionHasUser(sid)
+}