rst: Open thread core images without -nocheck

These are image files that weren't yet opened, thus should be
opened with proper checks.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

cr-restore.c

@@ -1644,7 +1644,7 @@ static int sigreturn_restore(pid_t pid, struct list_head *tgt_vmas, int nr_vmas)
 			continue;
 
 		/* Core files are to be opened */
-		thread_args[i].fd_core = open_image_ro_nocheck(FMT_FNAME_CORE, thread_args[i].pid);
+		thread_args[i].fd_core = open_image_ro(CR_FD_CORE, thread_args[i].pid);
 		if (thread_args[i].fd_core < 0)
 			goto err;
 

restorer.c

@@ -145,7 +145,6 @@ long restore_thread(struct thread_restore_args *args)
 
 	core_entry = (struct core_entry *)&args->mem_zone.heap;
 
-	sys_lseek(args->fd_core, MAGIC_OFFSET, SEEK_SET);
 	ret = sys_read(args->fd_core, core_entry, sizeof(*core_entry));
 	if (ret != sizeof(*core_entry)) {
 		write_num_n(__LINE__);