Fix negative write pool

[peterlimg]

Fixes

This issue should have been fixed via #2462 actually, it happens in similar way that tests submit lock transactions with negative transaction value, while before #2462, we don't validate the value and will put it to txn pool. In the txn processing code, we ignored the token converting error and emit event to update the allocation.write_pool, which will be fixed by this PR. Anyway, because the #2462, the transactions with invalid value will be ignored, that's why we don't see this error recently.

Changes

Need to be mentioned in CHANGELOG.md?

Tests

Tasks to complete before merging PR:

• Ensure system tests are passing. If not Run them manually to check for any regressions 📋
• Do any new system tests need added to test this change? do any existing system tests need updated? If so create a PR at 0chain/system_test
• Merge your system tests PR to master AFTER merging this PR

Associated PRs (Link as appropriate):

• blobber:
• gosdk:
• system_test:
• zboxcli:
• zwalletcli:
• Other: ...

[codecov-commenter]

Codecov Report

Merging #2484 (6b88afd) into staging (6cf4396) will increase coverage by 0.00%.
The diff coverage is 0.00%.

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@@           Coverage Diff            @@
##           staging    #2484   +/-   ##
========================================
  Coverage    28.83%   28.83%           
========================================
  Files          380      380           
  Lines        63754    63758    +4     
========================================
+ Hits         18384    18387    +3     
- Misses       43204    43213    +9     
+ Partials      2166     2158    -8     

Flag	Coverage Δ
Unit-Tests	28.83% <0.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...go/0chain.net/smartcontract/storagesc/writepool.go	3.96% <0.00%> (-0.17%)	⬇️

... and 4 files with indirect coverage changes

[dabasov]

lgtm