[#2203] shard: Do not panic in Close after unsuccessful Init

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

pkg/local_object_storage/shard/control.go

@@ -261,7 +261,10 @@ func (s *Shard) Close() error {
 		}
 	}
 
+	// If Init/Open was unsuccessful gc can be nil.
+	if s.gc != nil {
 		s.gc.stop()
+	}
 
 	return nil
 }