wormchain: tokenbridge: Check that the target chain is registered

Ensure that the destination chain has been registered in the tokenbridge
before allowing transfers to it.  This prevents users from accidentally
locking up their tokens in the token bridge by passing in an invalid
chain id.

wormhole_chain/x/tokenbridge/keeper/msg_server_transfer.go

@@ -26,6 +26,10 @@ func (k msgServer) Transfer(goCtx context.Context, msg *types.MsgTransfer) (*typ
 		return nil, err
 	}
 
+	if _, found := k.GetChainRegistration(ctx, msg.ToChain); !found {
+		return nil, types.ErrInvalidTargetChain
+	}
+
 	meta, found := k.bankKeeper.GetDenomMetaData(ctx, msg.Amount.Denom)
 	if !found {
 		return nil, types.ErrNoDenomMetadata