Assertion hit in httpclient
```
vendor/nim-websock/websock/types.nim(350) main
vendor/nim-websock/websock/types.nim(343) NimMain
beacon_chain/nimbus_validator_client.nim(199) main
vendor/nim-chronos/chronos/asyncloop.nim(1091) waitFor
vendor/nim-chronos/chronos/asyncloop.nim(279) poll
vendor/nim-chronos/chronos/asyncfutures2.nim(365) futureContinue
vendor/nim-presto/presto/client.nim(527) requestWithBody
vendor/nim-chronos/chronos/apps/http/httpclient.nim(1065) finish
vendor/nim-chronos/chronos/asyncfutures2.nim(365) futureContinue
vendor/nim-chronos/chronos/apps/http/httpclient.nim finish
vendor/nimbus-build-system/vendor/Nim/lib/system/assertions.nim(29) failedAssertImpl
vendor/nimbus-build-system/vendor/Nim/lib/system/assertions.nim(22) raiseAssert
vendor/nimbus-build-system/vendor/Nim/lib/system/fatal.nim(49) sysFatal
[[reraised from:
vendor/nim-websock/websock/types.nim(350) main
vendor/nim-websock/websock/types.nim(343) NimMain
beacon_chain/nimbus_validator_client.nim(199) main
vendor/nim-chronos/chronos/asyncloop.nim(1091) waitFor
vendor/nim-chronos/chronos/asyncloop.nim(279) poll
vendor/nim-chronos/chronos/asyncfutures2.nim(365) futureContinue
vendor/nim-presto/presto/client.nim(527) requestWithBody
vendor/nim-chronos/chronos/apps/http/httpclient.nim(1065) finish
vendor/nim-chronos/chronos/asyncfutures2.nim(387) futureContinue
]]
[[reraised from:
vendor/nim-websock/websock/types.nim(350) main
vendor/nim-websock/websock/types.nim(343) NimMain
beacon_chain/nimbus_validator_client.nim(199) main
vendor/nim-chronos/chronos/asyncloop.nim(1091) waitFor
vendor/nim-chronos/chronos/asyncloop.nim(279) poll
vendor/nim-chronos/chronos/asyncfutures2.nim(365) futureContinue
vendor/nim-chronos/chronos/asyncmacro2.nim(118) requestWithBody
]]
[[reraised from:
vendor/nim-websock/websock/types.nim(350) main
vendor/nim-websock/websock/types.nim(343) NimMain
beacon_chain/nimbus_validator_client.nim(199) main
vendor/nim-chronos/chronos/asyncloop.nim(1091) waitFor
vendor/nim-chronos/chronos/asyncloop.nim(279) poll
vendor/nim-chronos/chronos/asyncfutures2.nim(387) futureContinue
]]
Error: unhandled exception: /Users/jenkins/workspace/_nimbus-eth2_multibranch_PR-3529/macos_amd64/vendor/nim-chronos/chronos/apps/http/httpclient.nim(1072, 11) `request.connection.state == HttpClientConnectionState.RequestBodySending` Connection's state is RequestBodySent [AssertionError]
```
[log_val3.zip](https://github.com/status-im/nim-chronos/files/8314902/log_val3.zip)

Seen spuriously in Jenkins: https://ci.status.im/blue/organizations/jenkins/nimbus%2Fnimbus-eth2%2Fmultibranch/detail/PR-3529/1/pipeline