restore: check whether a thread core contains comm or not

  CC       criu/cr-restore.o
criu/cr-restore.c:3470:22: error: address of array 'thread_args[i].comm' will always evaluate to 'true' [-Werror,-Wpointer-bool-conversion]
                if (thread_args[i].comm)
                ~~  ~~~~~~~~~~~~~~~^~~~
1 error generated.
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

criu/cr-restore.c

@@ -3461,7 +3461,7 @@ static int sigreturn_restore(pid_t pid, struct task_restore_args *task_args, uns
 		if (construct_sigframe(sigframe, sigframe, blkset, tcore))
 			goto err;
 
-		if (thread_args[i].comm)
+		if (tcore->thread_core->comm)
 			strncpy(thread_args[i].comm, tcore->thread_core->comm, TASK_COMM_LEN);
 		else
 			strncpy(thread_args[i].comm, core->tc->comm, TASK_COMM_LEN);