efi_loader: fix efi_initrd_deregister()

Don't try to delete a non-existent handle.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/lib/efi_loader/efi_load_initrd.c b/lib/efi_loader/efi_load_initrd.c
index c5e6652..3d6044f 100644
--- a/lib/efi_loader/efi_load_initrd.c
+++ b/lib/efi_loader/efi_load_initrd.c
@@ -230,6 +230,9 @@
  */
 void efi_initrd_deregister(void)
 {
+	if (!efi_initrd_handle)
+		return;
+
 	efi_delete_handle(efi_initrd_handle);
 	efi_initrd_handle = NULL;
 }