files: make convert_path_from_another_mp always return relative path

If dmi->ns_mountpoint is "/" then in dst we will return "/..." -
absolute path but we want here path relative to dmi mount. Adding "./"
before the path guaranties that it will be always relative.

https://jira.sw.ru/browse/PSBM-72351Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

criu/files-reg.c

@@ -1347,7 +1347,7 @@ static void convert_path_from_another_mp(char *src, char *dst, int dlen,
 	 * Absolute path to the mount point + difference between source
 	 * and destination roots + path relative to the mountpoint.
 	 */
-	snprintf(dst, dlen, "%s/%s/%s",
+	snprintf(dst, dlen, "./%s/%s/%s",
 				dmi->ns_mountpoint + 1,
 				smi->root + strlen(dmi->root),
 				src + off);