x86/HAP: adjust monitor table related error handling

x86/HAP: adjust monitor table related error handling

hap_make_monitor_table() will return INVALID_MFN if it encounters an
error condition, but hap_update_paging_modes() wasn’t handling this
value, resulting in an inappropriate value being stored in
monitor_table. This would subsequently misguide at least
hap_vcpu_teardown(). Avoid this by bailing early.

Further, when a domain has/was already crashed or (perhaps less
important as there's no such path known to lead here) is already dying,
avoid calling domain_crash() on it again - that's at best confusing.

This is part of CVE-2022-33746 / XSA-410.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>