WSEMUL_DEFAULT instant hard reset on boot

[der Mouse <mouse%Rodents-Montreal.ORG@localhost>]

Thanks to a botch when playing with kernel configs, I discovered the
hard way that setting WSEMUL_DEFAULT to a name that does not name an
emulation the kernel has leads to an instant hard reset at boot -
booter loads the kernel and bam, I'm looking at the BIOS POST screen.
(This is with 5.1, but I suspect other versions will do similar
things.)

Seems to me picking almost anything else would be better - first
emulation on the list, even, would be better than an instant reset.
Thoughts?  Worth a PR?

/~\ The ASCII                             Mouse
\ / Ribbon Campaign
 X  Against HTML                mouse%rodents-montreal.org@localhost
/ \ Email!           7D C8 61 52 5D E7 2D 39  4E F1 31 3E E8 B3 27 4B