efi_loader: Fix potential deref-after-null

After having been compared to a NULL value at efi_disk.c:426,
pointer 'part_info' is dereferenced at efi_disk.c:534.

Signed-off-by: Maks Mishin <maks.mishinFZ@gmail.com>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
1 file changed