Improve some lock handling under panics

t.go

@@ -85,8 +85,8 @@ func (t *Torrent) PieceBytesMissing(piece int) int64 {
 // or connected peers.
 func (t *Torrent) Drop() {
 	t.cl.lock()
+	defer t.cl.unlock()
 	t.cl.dropTorrent(t.infoHash)
-	t.cl.unlock()
 }
 
 // Number of bytes of the entire torrent we have completed. This is the sum of

torrent.go

@@ -741,9 +741,11 @@ func (t *Torrent) close() (err error) {
 	t.closed.Set()
 	t.tickleReaders()
 	if t.storage != nil {
-		t.storageLock.Lock()
-		t.storage.Close()
-		t.storageLock.Unlock()
+		func() {
+			t.storageLock.Lock()
+			defer t.storageLock.Unlock()
+			t.storage.Close()
+		}()
 	}
 	t.iterPeers(func(p *Peer) {
 		p.close()