tgrade-valset: Wrong automatic jailing logic

[maurolacy]

If verify_validators is enabled, non-signing validators must be jailed only if they are not already jailed. If not, it'll be effectively impossible for them to get out of jail, because their jailing expiration date will be continuously moved forward.

poe-contracts/contracts/tgrade-valset/src/contract.rs

Lines 712 to 713 in 5c1ac97

	// validator is inactive for at least MISSED_BLOCKS, jail!
	JAIL.save(deps.storage, operator_addr, &expiration)

Write a test to confirm / reproduce this bug, and the fix.

[maurolacy]

Closing as not needed / already solved (see #187).