fix view key corruption

[auruya]

Since the output scanning is done in parallel to key image calculation now, we sometimes get a scrambled view key due to a race condition where view key gets read by scan job between the time we encrypt view key before decrypting all keys. This PR adds a couple of new functions to account_keys that excludes view key encryption/decryption directly instead of encrypting/decrypting it each time.

[jeffro256]

This is the job of the wallet2::m_encrypt_keys_after_refresh. If the view-key is being mangled during refresh, then the lifetime of m_encrypt_keys_after_refresh isn't correct. That's where the fix should be IMO

[auruya]

@jeffro256 yes that can be another way to solve it. If that is preferred, I think this scan_key_image call

monero/src/wallet/wallet2.cpp

Line 3651 in 18b0c9f

scan_key_image(*enote_scan_infos.at(i), /*pool=*/false, output_key_images[i], password_failure);

should be moved after

monero/src/wallet/wallet2.cpp

Line 3673 in 18b0c9f

if (!scan_blocks_waiter.wait())

this waiter so that we know no thread is using the view key. Of course this will impact the performance but to reduce the impact we can still do the scan_key_image in parallel.