[PATCH] replication: fix a failing assert in replica_on_applier_disconnect()

[Vladimir Davydov]

Looks good.

On Fri, Aug 03, 2018 at 08:59:05AM +0300, Serge Petrenko wrote:
> One possible case when two applier errors happen one after another
> wasn't handled in replica_on_applier_disconnect(), which lead to
> occasional test failures and crashes. Handle this case.
> 
> Part of #3510
> ---
> This patch fixes an assertion fail, submitted by @locker in issue comments.
> I wasn't able to reproduce 2 failures reported in the issue itself, and asked
> for comments, but got no answer. I also couldn't fix the latter 2
> failures just by looking at code.
> 
> https://github.com/tarantool/tarantool/tree/sergepetrenko/gh-3510-replication-asserts-fail
> https://github.com/tarantool/tarantool/issues/3510
> 
>  src/box/replication.cc | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/src/box/replication.cc b/src/box/replication.cc
> index 26bbbe32a..0efbd7c0e 100644
> --- a/src/box/replication.cc
> +++ b/src/box/replication.cc
> @@ -350,6 +350,10 @@ replica_on_applier_disconnect(struct replica *replica)
>  		assert(replicaset.applier.connected > 0);
>  		replicaset.applier.connected--;
>  		break;
> +	case APPLIER_LOADING:
> +		assert(replicaset.applier.loading > 0);
> +		replicaset.applier.loading--;
> +		break;
>  	case APPLIER_DISCONNECTED:
>  		break;
>  	default: