fix wrong volume count

fix https://github.com/chrislusf/seaweedfs/issues/1013

weed/storage/erasure_coding/ec_shard.go

@@ -81,7 +81,7 @@ func (shard *EcVolumeShard) Close() {
 
 func (shard *EcVolumeShard) Destroy() {
 	os.Remove(shard.FileName() + ToExt(int(shard.ShardId)))
-	stats.VolumeServerVolumeCounter.WithLabelValues(shard.Collection, "ec_shards").Inc()
+	stats.VolumeServerVolumeCounter.WithLabelValues(shard.Collection, "ec_shards").Dec()
 }
 
 func (shard *EcVolumeShard) ReadAt(buf []byte, offset int64) (int, error) {

weed/storage/volume_vacuum.go

@@ -53,7 +53,7 @@ func (v *Volume) CommitCompact() error {
 		glog.V(0).Infof("fail to close volume %d", v.Id)
 	}
 	v.dataFile = nil
-	stats.VolumeServerVolumeCounter.WithLabelValues(v.Collection, "volume").Inc()
+	stats.VolumeServerVolumeCounter.WithLabelValues(v.Collection, "volume").Dec()
 
 	var e error
 	if e = v.makeupDiff(v.FileName()+".cpd", v.FileName()+".cpx", v.FileName()+".dat", v.FileName()+".idx"); e != nil {