Overabundant balance check for bid_collateral_operation

[abitmore]

Bug Description

bitshares-core/libraries/chain/market_evaluator.cpp

Lines 394 to 399 in 71641eb

	if( o.additional_collateral.amount > 0 )
	{
	FC_ASSERT( d.get_balance(*_paying_account, _bitasset_data->options.short_backing_asset(d)) >= o.additional_collateral,
	"Cannot bid ${c} collateral when payer only has ${b}", ("c", o.additional_collateral.amount)
	("b", d.get_balance(*_paying_account, o.additional_collateral.asset_id(d)).amount) );
	}

• If a bidder is creating a new bid, this check is fine;
• if a bidder is updating an old bid, this check doesn't make sense but only annoying, actually we should check balance + old_bid_collateral >= new_bid_collateral, because the old bid will be cancelled so collateral will be released then can be used in the new bid. Additionally, balance will be checked when calling adjust_balance() later, so the check here is not necessary.

Fixing this requires a consensus upgrade.

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

• 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.)
• UX (the User Experience)
• Other (please add below)

Steps To Reproduce
Steps to reproduce the behavior (example outlined below):

1. globally settle asset USD;
2. fund account test with 10000 BTS;
3. bid with 9000 BTS;
4. try to update the bid to 8000 BTS, fail.

Expected Behavior
Able to update bid when balance + old_bid_collateral >= new_bid_collateral.

Screenshots (optional)
If applicable, add screenshots to help explain process flow and behavior.

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

• Host OS: [e.g. Ubuntu 18.04 LTS]
• Host Physical RAM [e.g. 4GB]
• BitShares Version: [e.g. 2.0.180425]
• OpenSSL Version: [e.g. 1.1.0g]
• Boost Version: [e.g. 1.65.1]

Additional Context (optional)
Add any other context about the problem here.

CORE TEAM TASK LIST

• Evaluate / Prioritize Bug Report
• Refine User Stories / Requirements
• Define Test Cases
• Design / Develop Solution
• Perform QA/Testing
• Update Documentation

[pmconrad]

Fixed by #1830