Fix consumer handling in pallet balances update_locks

[bkchr]

When removing all locks of an account there is a bug that leads to reducing the consumer count twice.

First it happens here:

polkadot-sdk/substrate/frame/balances/src/lib.rs

Line 969 in f0ab54e

frame_system::Pallet::<T>::dec_consumers(who);

And then the second time here:

polkadot-sdk/substrate/frame/balances/src/lib.rs

Line 1072 in f0ab54e

system::Pallet::<T>::dec_consumers(who);

[liamaharon]

Self-assigned, I need to spend some time understanding this for writing docs anyway.

[xlc]

we need a script to check if this bug have happened on any parachain and generate a list of accounts that needs fix up

[xlc]

and this is something should be identified by a fuzzer so I guess we don’t have enough of them

[xlc]

I can image it could be hard to write such script that works on all the parachains. That should spark another question: What can we improve to make such task easier in future? e.g. better event system or better indexer or better invariant checker

[bkchr]

Writing a script for every chain should be possible. You just need to monitor pallet_balances::Lock and the changes to consumers. We would probably only require teams to set the starting block for when the runtime was activated that contained the broken logic.

[michalisFr]

@bkchr Does this relate to this issue? #1404 (comment)

[bkchr]

@bkchr Does this relate to this issue? #1404 (comment)

Could probably be related.