ICS20: fix port and add assertions for packet data (#1046)

* ics20 nits

* fix assertion

spec/app/ics-020-fungible-token-transfer/README.md

@@ -88,7 +88,7 @@ The `setup` function must be called exactly once when the module is created (per
 
 ```typescript
 function setup() {
-  capability = routingModule.bindPort("bank", ModuleCallbacks{
+  capability = routingModule.bindPort("transfer", ModuleCallbacks{
     onChanOpenInit,
     onChanOpenTry,
     onChanOpenAck,
@@ -257,6 +257,11 @@ function sendFungibleTokens(
 ```typescript
 function onRecvPacket(packet: Packet) {
   FungibleTokenPacketData data = packet.data
+  assert(data.denom !== "")
+  assert(data.amount > 0)
+  assert(data.sender !== "")
+  assert(data.receiver !== "")
+
   // construct default acknowledgement of success
   FungibleTokenPacketAcknowledgement ack = FungibleTokenPacketAcknowledgement{true, null}
   prefix = "{packet.sourcePort}/{packet.sourceChannel}/"