files-reg: fix use-after-free in open_remap_ghost()

Ghost file entry used right after it has been freed:
	ERROR: AddressSanitizer: heap-use-after-free on address 0x60700000dc50
	READ of size 4 at 0x60700000dc50 thread T0
	    #0 0x46e819 in open_remap_ghost criu/files-reg.c:312
	    #1 0x46e819 in prepare_one_remap criu/files-reg.c:461
	    #2 0x46e819 in prepare_remaps criu/files-reg.c:507
	    checkpoint-restore#3 0x45af00 in root_prepare_shared criu/cr-restore.c:235
	    checkpoint-restore#4 0x45af00 in restore_task_with_children criu/cr-restore.c:1421
	    checkpoint-restore#5 0x7efc71e85f0c in clone (/lib64/libc.so.6+0xe7f0c)

	0x60700000dc50 is located 32 bytes inside of 80-byte region [0x60700000dc30,0x60700000dc80)
	freed by thread T0 here:
	    #0 0x7efc7305184a in __interceptor_free (/usr/lib/gcc/x86_64-pc-linux-gnu/5.4.0/libasan.so.2+0x9884a)
	    #1 0x46e4df in open_remap_ghost criu/files-reg.c:309
	    #2 0x46e4df in prepare_one_remap criu/files-reg.c:461
	    checkpoint-restore#3 0x46e4df in prepare_remaps criu/files-reg.c:507

	previously allocated by thread T0 here:
	    #0 0x7efc73051b82 in malloc (/usr/lib/gcc/x86_64-pc-linux-gnu/5.4.0/libasan.so.2+0x98b82)
	    #1 0x7efc7277a8ea in protobuf_c_message_unpack (/usr/lib64/libprotobuf-c.so.1+0x48ea)
	    #2 0xd528232002838017  (<unknown module>)

Just move freeing after the last 'gfe' usage to fix this.

Fixes: d0097b2 ("files: Support ghost directories restore")
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>

criu/files-reg.c

@@ -306,12 +306,13 @@ static int open_remap_ghost(struct reg_file_info *rfi,
 	if (create_ghost(gf, gfe, img))
 		goto close_ifd;
 
-	ghost_file_entry__free_unpacked(gfe, NULL);
 	close_image(img);
 
 	gf->remap.is_dir = S_ISDIR(gfe->mode);
 	gf->remap.uid = gfe->uid;
 	gf->remap.gid = gfe->gid;
+	ghost_file_entry__free_unpacked(gfe, NULL);
+
 	return 0;
 
 close_ifd: