fix(v2.10) missing tx encoder

[javiersuweijie]

In the logs that validators submit, there was an error whenever the validator proposes the block.

ERR panic recovered in PrepareProposal height=9446424 module=server panic="runtime error: invalid memory address or nil pointer dereference

This is caused by a nil txEncoder.

https://github.com/terra-money/cosmos-sdk/blob/c27c7fcc5cf76253a2cbeba2270736ae432d1478/baseapp/baseapp.go#L882

It panics and gets caught in the abci.go

https://github.com/terra-money/cosmos-sdk/blob/c27c7fcc5cf76253a2cbeba2270736ae432d1478/baseapp/abci.go#L279-L290

And returns the proposal without actually running through the antehandlers for tx validation. Therefore, when preparing a proposal, the txs in it are never actually checked and if any of the transactions fail in ProcessProposal, the proposal is invalid and rejected.

If the same set of invalid transactions are included in the block proposed by most of the validators, the chain halts.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.46%. Comparing base (1e81e02) to head (41c2ca6).
Report is 1 commits behind head on release/v2.10.

Additional details and impacted files

@@                Coverage Diff                @@
##           release/v2.10     #291      +/-   ##
=================================================
+ Coverage          70.45%   70.46%   +0.01%     
=================================================
  Files                 45       45              
  Lines               2095     2096       +1     
=================================================
+ Hits                1476     1477       +1     
  Misses               452      452              
  Partials             167      167              

Files	Coverage Δ
app/app.go	74.70% <100.00%> (+0.14%)	⬆️