Fix DecCoins Bugs

[alexanderbez]

• Panic on zero decimal input
• Don't include zero decimal coins in results
• Add TOC to CHANGELOG to make it easier to navigate and add entries when working against release branches.

closes: #4050

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• Targeted PR against correct branch (see CONTRIBUTING.md)

• Linked to github-issue with discussion and accepted design OR link to spec that describes this work.

• Wrote tests

• Updated relevant documentation (docs/)

• Added a relevant changelog entry: sdkch add [section] [stanza] [message]

• rereviewed Files changed in the github PR explorer

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For Admin Use:

• Added appropriate labels to PR (ex. wip, ready-for-review, docs)
• Reviewers Assigned
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)

[codecov]

Codecov Report

Merging #4058 into release/v0.34.0 will increase coverage by <.01%.
The diff coverage is 27.27%.

@@                 Coverage Diff                 @@
##           release/v0.34.0    #4058      +/-   ##
===================================================
+ Coverage               60%   60.01%   +<.01%     
===================================================
  Files                  212      212              
  Lines                15111    15121      +10     
===================================================
+ Hits                  9068     9075       +7     
- Misses                5420     5423       +3     
  Partials               623      623

[fedekunze]

LGTM

[cwgoes]

These changes look fine, but I don't think they cover all the cases:

• Couldn't Mul on line 321 also return 0 if the multiplied-by decimal is small?
• DecCoin bugs #4050 mentions that ParseDecCoins needs to be changed, but I don't think it does, since it calls IsValid() - maybe we could add a testcase though

[alexanderbez]

@cwgoes

Couldn't Mul on line 321 also return 0 if the multiplied-by decimal is small?

Yes, fixed.

#4050 mentions that ParseDecCoins needs to be changed, but I don't think it does, since it calls IsValid() - maybe we could add a testcase though

Yes, I mentioned that in the issue. I don't see how it's broken.