kvm tool: Don't close not yet opened files and SIGSEV fix

In case if there error happened in kvm__init and we have
no files opened -- we should not try to close them.

Also once kvm failed to init the caller should not try
to dereference a pointer obtained, otherwise we might get
SIGSEV

 | [cyrill@moon kvm]$ ./lkvm run ...
 | Error: '/dev/kvm' not found. Please make sure your kernel has CONFIG_KVM
 | enabled and that the KVM modules are loaded.
 | Segmentation fault (core dumped)
 | [cyrill@moon kvm]$

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>