kgdb crashes when remote debugging requested

[Jordan Gordeev <jgordeev@xxxxxx>]

kgdb crashes when remote debugging (-r) is requested. The crash involves 
a NULL pointer dereference in libkvm.
I've found that the crash was introduced with revision 1.2 of 
src/gnu/usr.bin/gdb/kgdb/kgdb.c.
In that revision the global variable 'kvm' isn't initialised if remote 
debugging is requested, however it is always used. The value of 'kvm' is 
passed to a libkvm function which attempts to dereference it.