grpcdb: close Iterator/ReverseIterator after use (#3424)

Fixes #3402

CHANGELOG_PENDING.md

@@ -47,3 +47,4 @@ Special thanks to external contributors on this release:
 - [libs/pubsub] \#951, \#1880 use non-blocking send when dispatching messages [ADR-33](https://github.com/tendermint/tendermint/blob/develop/docs/architecture/adr-033-pubsub.md)
 - [p2p] \#3369 do not panic when filter times out
 - [cmd] \#3408 Fix `testnet` command's panic when creating non-validator configs (using `--n` flag) (@srmo)
+- [libs/db/remotedb/grpcdb] \#3402 Close Iterator/ReverseIterator after use

libs/db/remotedb/grpcdb/server.go

@@ -138,6 +138,7 @@ func (s *server) SetSync(ctx context.Context, in *protodb.Entity) (*protodb.Noth
 
 func (s *server) Iterator(query *protodb.Entity, dis protodb.DB_IteratorServer) error {
 	it := s.db.Iterator(query.Start, query.End)
+	defer it.Close()
 	return s.handleIterator(it, dis.Send)
 }
 
@@ -162,6 +163,7 @@ func (s *server) handleIterator(it db.Iterator, sendFunc func(*protodb.Iterator)
 
 func (s *server) ReverseIterator(query *protodb.Entity, dis protodb.DB_ReverseIteratorServer) error {
 	it := s.db.ReverseIterator(query.Start, query.End)
+	defer it.Close()
 	return s.handleIterator(it, dis.Send)
 }