THORChain is accepting pending add liquidity for assets without corresponding gas asset pools

As described in this Discord thread and the #midgard channel conversation that spawned it,
the Flipside query

SELECT *
FROM thorchain.pending_liquidity_events
WHERE (pool_name LIKE '%OR.A%')
  OR (pool_name LIKE '%or.a%')
ORDER BY block_id DESC

returns 29 rows, including rows for THOR.AVAX.AVAX .

Given that a token cannot be migrated in a churn without a gas asset pool to pay for its transaction fee,
I currently propose this be resolved by checking in add liquidity validation that non-gas-asset destination asset already has an existing external-chain gas asset pool.
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As no THOR.RUNE gas asset pool exists, this would reject THOR. destination assets as well as any memos for unrecognised chains.

I further suggest that Ragnarok status be checked, to reject add liquidity to a currently-Ragnaroked pool (whether token like TERRA.UST or gas asset pool like TERRA.LUNA).

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For a less specific example,

SELECT *
FROM thorchain.pending_liquidity_events
WHERE (pool_name LIKE 'THOR%')
ORDER BY block_id DESC

returns 36 rows, including for THOR.BTC.BTC (add blocks 4612128 and 4612334, withdraw block 4625696)
and THOR.ETH which still has 2 RUNE pending for it at time of writing.