Fix data race setting v2 piece hash

piece.go

@@ -286,7 +286,10 @@ func (p *Piece) mustGetOnlyFile() *File {
 func (p *Piece) setV2Hash(v2h [32]byte) {
 	// See Torrent.onSetInfo. We want to trigger an initial check if appropriate, if we didn't yet
 	// have a piece hash (can occur with v2 when we don't start with piece layers).
-	if !p.hashV2.Set(v2h).Ok && p.hash == nil {
+	p.t.storageLock.Lock()
+	oldV2Hash := p.hashV2.Set(v2h)
+	p.t.storageLock.Unlock()
+	if !oldV2Hash.Ok && p.hash == nil {
 		p.t.updatePieceCompletion(p.index)
 		p.t.queueInitialPieceCheck(p.index)
 	}