commands/swarm(fix): handle empty multiaddrs

These are technically valid at the moment so they aren't caught when calling
`NewMultiaddr`. See multiformats/go-multiaddr#104.

fixes #6354

core/commands/swarm.go

@@ -509,12 +509,17 @@ func resolveAddresses(ctx context.Context, addrs []string) ([]ma.Multiaddr, erro
 
 	maddrC := make(chan ma.Multiaddr)
 
-	for _, addr := range addrs {
+	for i, addr := range addrs {
 		maddr, err := ma.NewMultiaddr(addr)
 		if err != nil {
 			return nil, err
 		}
 
+		// only way to check for "empty" multiaddrs at the moment.
+		if len(maddr.Bytes()) == 0 {
+			return nil, fmt.Errorf("multiaddr %d is empty", i)
+		}
+
 		// check whether address ends in `ipfs/Qm...`
 		if _, last := ma.SplitLast(maddr); last.Protocol().Code == ma.P_IPFS {
 			maddrs = append(maddrs, maddr)