Fix check for open_image() ret

When open_image() was modified to return a pointer rather than an int
in commit 295090c1, these two checks were overlooked and never fixed.
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Acked-by: Andrew Vagin <avagin@odin.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

files-reg.c

@@ -340,7 +340,7 @@ static int dump_ghost_file(int _fd, u32 id, const struct stat *st, dev_t phys_de
 	pr_info("Dumping ghost file contents (id %#x)\n", id);
 
 	img = open_image(CR_FD_GHOST_FILE, O_DUMP, id);
-	if (img < 0)
+	if (!img)
 		return -1;
 
 	gfe.uid = userns_uid(st->st_uid);

mount.c

@@ -2199,7 +2199,7 @@ static int collect_mnt_from_image(struct mount_info **pms, struct ns_id *nsid)
 	char root[PATH_MAX] = ".";
 
 	img = open_image(CR_FD_MNTS, O_RSTR, nsid->id);
-	if (img < 0)
+	if (!img)
 		return -1;
 
 	if (nsid->id != root_item->ids->mnt_ns_id)