get_tx_height previously did not consider whether the walletDB has the full tx for
the corresponding txid, and could consider a tx even "mined" and spv-ed, even if
we were missing the raw tx.
Now if the full tx is missing or the tx in the db is partial,
get_tx_height considers it to be LOCAL.
In particular the txbatcher, in `run_iteration`,
- first saves a tx as local *unsigned* (to reserve UTXOs),
- then signs it and tries to broadcast it.
The history tx will later transition to local and signed,
after we get back the broadcasted tx via the Synchronizer dance.
In the meantime there is a race where we have an unsigned tx in the history,
but the txid could already transition to mempool or even to mined,
before we download the full raw tx from the server.
During that time window, it makes the adb state more consistent
to just consider the history tx to be local, as done here.
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