CRM-20611: fix financial records of cancelled line_items on event fee change selection

[monishdeb]

• CRM-20611: Cancelling a line-item by changing fee selection of event, leads to incorrect financial records

[monishdeb]

@pradpnayak can you please QA this PR!!

[pradpnayak]

@monishdeb i did some qa, but i still found an entry with net_amount not set properly

Steps :

1. Added participant to Fall Fundraiser Dinner Event by selecting option 'Family - $ 200.00' (trxn id 1 & 2 from image)
2. I did change selection from 'Family - $ 200.00' to Couple - $ 100.00(trxn id 3) -- still not fixed
3. Recorded refund (trxn id 4)

Before Patch db entries

After Patch db entries

[monishdeb]

@pradpnayak thanks for your feedback. I have updated PR with the fix. Please have a look!

[pradpnayak]

QA'd, working fine

[colemanw]

Looks like a clean bugfix. It includes a test and has been manually tested as well. Merging.