Save rewards only if miner exists in the network

[lpoli]

Fixes

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 #2358 (d35cec9) into staging (afbbb96) will increase coverage by 0.00%.
The diff coverage is 33.33%.

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@@           Coverage Diff            @@
##           staging    #2358   +/-   ##
========================================
  Coverage    28.97%   28.98%           
========================================
  Files          377      377           
  Lines        63034    63036    +2     
========================================
+ Hits         18267    18268    +1     
- Misses       42617    42619    +2     
+ Partials      2150     2149    -1     

Flag	Coverage Δ
Unit-Tests	28.98% <33.33%> (+<0.01%)	⬆️

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

Impacted Files	Coverage Δ
code/go/0chain.net/smartcontract/minersc/fees.go	30.71% <33.33%> (+0.33%)	⬆️

... and 3 files with indirect coverage changes

[dabasov]

lgtm

[peterlimg]

getRewardedMiner does not return error if the error was 'node not found', we should not continue to get random miner from minerList when it happens, as if other miners can get. the miner successfully, they will result in different MPT state due to the different miner they selected for rewarding.