page-read: fix open_page_read usage

1. Fix uninitialized use of pr in cr_dedup_one_pagemap and get_page:
https://github.com/xemul/criu/issues/178
2. In ud_open, close pr in case of error returned from find_vmas->
collect_uffd_pages as we free lpi with lpi->pr open; so need check in
lpi_fini if uffd is >0 before close

v2:rebase to new criu-dev
Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Acked-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

criu/cr-dedup.c

@@ -75,10 +75,8 @@ static int cr_dedup_one_pagemap(int id, int flags)
 
 	flags |= PR_MOD;
 	ret = open_page_read(id, &pr, flags);
-	if (ret <= 0) {
-		ret = -1;
-		goto exit;
-	}
+	if (ret <= 0)
+		return -1;
 
 	prp = pr.parent;
 	if (!prp)