Bootstrap error message on non-existent sandbox

[dimensionv]

When you run

# pkg_comp -c <config> bootstrap

and you forgot to create the sandbox beforehand, it will give you a very misleading error message about a missing real path on mount (the error message is of course correct, but only a follow up of the actual root cause, the missing sandbox).
It would be great if there would be a sandbox-detection routine to either create the sandbox on the fly if it doesn't exist on calling bootstrap, or to at least give the user a proper error message like "please run pkg_comp -c sandbox-create, first".