console: check that ST->ConIn and ST->ConOut are non-NULL
console: check that ST->ConIn and ST->ConOut are non-NULL

There's been some discussion on how to handle machines without console
devices.  The consensus so far has been that they should have dummy
ConOut implementations, but that means the first vendor to build a
machine without asking around is in for some surprises.

This patch makes the places where our console library uses ST->ConIn or
ST->ConOut check that they're present before doing so.

Signed-off-by: Peter Jones <2e0a021e603479ff81838c00c3b770daca4e0214@redhat.com>

rhinstaller/shim,rhinstaller/shim,rhinstaller/shim