make evm_log_* fields null for non evm.log events

[Andrew7234]

While cleaning up the evm_log_* fields in #632 I noticed that these fields weren't properly set to null. evm_log_name was set to the empty string and evm_log_signature was set to a zero bytestring.

Note: This PR does not include a migration to retroactively set existing fields to null. The queries to do this take on the order of 24hrs to run, which would be unacceptable downtime for any prod deployment. Instead, we should run the following queries manually

UPDATE chain.runtime_events
SET
	evm_log_name = NULL
WHERE
	evm_log_name = '';

UPDATE chain.runtime_events
SET
	evm_log_signature = NULL
WHERE
	evm_log_signature = decode('0000000000000000000000000000000000000000000000000000000000000000', 'hex');

Testing: Manually ran the indexer and confirmed that there were no rows where evm_log_* was non-null for any non evm.log events.

select * from chain.runtime_events where type != 'evm.log' and evm_log_signature is not null limit 10;

[mitjat]

nice 👍