`operation_history_object::virtual_op` numbering may be discontinuous (possibly with holes)

Bug Description

In database::push_applied_operation(), after _current_virtual_op is assigned to virtual_op of the newly created operation_history_object, _current_virtual_op++ is called: https://github.com/bitshares/bitshares-core/blob/f812666bb3bb884f6e8e5e7e669dc0050d3f3a69/libraries/chain/db_block.cpp#L535-L544

If the operation being pushed is in a proposal, after it is added to _applied_ops, it may be removed later if the proposal fails, but _current_virtual_op is not updated back: https://github.com/bitshares/bitshares-core/blob/f812666bb3bb884f6e8e5e7e669dc0050d3f3a69/libraries/chain/db_block.cpp#L361-L364

I'm not sure if it is worth fixing.

Impacts Describe which portion(s) of BitShares Core may be impacted by this bug. Please tick at least one box.

[x] API (the application programming interface)
[ ] Build (the build process or something prior to compiled code)
[ ] CLI (the command line wallet)
[ ] Deployment (the deployment process after building such as Docker, Travis, etc.)
[ ] DEX (the Decentralized EXchange, market engine, etc.)
[ ] P2P (the peer-to-peer network for transaction/block propagation)
[ ] Performance (system or user efficiency, etc.)
[ ] Protocol (the blockchain logic, consensus, validation, etc.)
[ ] Security (the security of system or user data, etc.)
[x] UX (the User Experience)
[ ] Other (please add below)

Host Environment Please provide details about the host environment. Much of this information can be found running: witness_node --version.

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