abci: fix socket client error for state sync responses

[erikgrinaker]

This caused the node to crash whenever any state sync-related request was called via the ABCI UNIX socket client.

[codecov]

Codecov Report

Merging #5395 into master will increase coverage by 0.37%.
The diff coverage is 39.50%.

@@            Coverage Diff             @@
##           master    #5395      +/-   ##
==========================================
+ Coverage   60.83%   61.21%   +0.37%     
==========================================
  Files         203      259      +56     
  Lines       20526    23415    +2889     
==========================================
+ Hits        12488    14334    +1846     
- Misses       6961     7617     +656     
- Partials     1077     1464     +387     

Impacted Files	Coverage Δ
abci/client/grpc_client.go	0.00% <0.00%> (ø)
abci/example/kvstore/persistent_kvstore.go	40.49% <0.00%> (-5.22%)	⬇️
blockchain/v0/pool.go	76.38% <0.00%> (-2.28%)	⬇️
blockchain/v2/processor_context.go	68.00% <0.00%> (+4.84%)	⬆️
cmd/tendermint/commands/lite.go	19.16% <0.00%> (-0.35%)	⬇️
cmd/tendermint/commands/reset_priv_validator.go	3.44% <0.00%> (-2.44%)	⬇️
cmd/tendermint/commands/run_node.go	0.00% <0.00%> (ø)
config/toml.go	60.97% <ø> (-4.99%)	⬇️
consensus/replay_file.go	0.00% <0.00%> (ø)
consensus/replay_stubs.go	57.57% <ø> (-3.30%)	⬇️
... and 289 more