efi: Handle NULL return value when getting loaded image protocol

efi: Handle NULL return value when getting loaded image protocol

The EFI spec mandates that the handle produced by the LoadImage boot
service has a LoadedImage protocol instance installed on it, but for
robustness, we should still deal with a NULL return value from the
helper routine that obtains this protocol pointer.

If this happens, don't try to start the image but unload it and return
an error.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>