moused,syscons: Avoid warning if system has no /dev/ttyv*

[emaste]

Summary

A VM had no virtual terminals and emitted a warning on boot
`eval: cannot open /dev/ttyv*: No such file or directory`.
 
Break the loop in this case to avoid the warning.
 
PR:             289173

[jlduran]

Just an optional suggestion (should be done on all three cases, of course).

libexec/rc/rc.d/moused

73

[michaelo]

I agree with @jlduran, all three should be covered. I applied the patch locally and the issue is gone.

Same issue exists in 14 and 13. I guess should be MFC'ed.

[emaste]

Thanks @michaelo for your review, I pushed before seeing the update in the review. I will MFC in a few days or a week.