Wrong denom "undefined" is showed in delegate and undelegate transactions

[mariopino]

Summary of Bug

Wrong denom "undefined" is showed in delegate and undelegate transactions in REST api.

Version

Steps to Reproduce

Example transaction:

https://stargate.cosmos.network/txs?action=begin_unbonding&delegator=cosmos16wgw3k7rspegl9khx79fuaa37unf4nfmxf7pyr

Extract of response (see cosmos-sdk/MsgUndelegate msg):

...
    "tx":{
      "type":"auth/StdTx",
      "value":{
        "msg":[
          {
            "type":"cosmos-sdk/MsgUndelegate",
            "value":{
              "delegator_address":"cosmos16wgw3k7rspegl9khx79fuaa37unf4nfmxf7pyr",
              "validator_address":"cosmosvaloper1sjllsnramtg3ewxqwwrwjxfgc4n4ef9u2lcnj0",
              "amount":{
                "denom":"undefined",
                "amount":"100000"
              }
            }
          }
        ],
...

Redelegate example (same behaviour):

https://stargate.cosmos.network/txs?action=begin_redelegate&delegator=cosmos16wgw3k7rspegl9khx79fuaa37unf4nfmxf7pyr

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[faboweb]

Fixed in: #4600