efi_loader: efi_dp_part_node check dp_alloc return value

dp_alloc() may return NULL. This needs to be caught.

Fixes: 98d48bdf41 ("efi_loader: provide a function to create a partition node")
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>

lib/efi_loader/efi_device_path.c

@@ -936,7 +936,8 @@ struct efi_device_path *efi_dp_part_node(struct blk_desc *desc, int part)
 		dpsize = sizeof(struct efi_device_path_hard_drive_path);
 	buf = dp_alloc(dpsize);
 
-	dp_part_node(buf, desc, part);
+	if (buf)
+		dp_part_node(buf, desc, part);
 
 	return buf;
 }