Do not return -1 if no access to kernel file (RhBug:1443344)
Do not return -1 if no access to kernel file (RhBug:1443344)

If used systemd-boot as the EFI bootloader, the file
/boot/vmlinuz-<kernel_version> is relocated, therefore detection fails.

https://bugzilla.redhat.com/show_bug.cgi?id=1443344

Closes: #285
Approved by: ignatenkobrain

edynox/libdnf,rpm-software-management/libhif,hughsie/libhif,rpm-software-management/libdnf,Conan-Kudo/libhif,hughsie/libhif,rpm-software-management/libdnf,Conan-Kudo/libhif,edynox/libdnf,edynox/libdnf,hughsie/libhif,hughsie/libhif,rpm-software-management/libhif,rpm-software-management/libdnf,rpm-software-management/libhif,Conan-Kudo/libhif,edynox/libdnf,rpm-software-management/libhif,rpm-software-management/libdnf,Conan-Kudo/libhif