Contract reader: fix int type output

[vbaranov]

Motivation

Resolve Internal server error caused by Int(x) type "0" value in the output of the contract method

Checklist for your Pull Request (PR)

• I added an entry to CHANGELOG.md with this PR
• If I added new functionality, I added tests covering it.
• If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.
• I checked whether I should update the docs and did so by submitting a PR to https://github.com/blockscout/docs
• If I added/changed/removed ENV var, I submitted a PR to https://github.com/blockscout/docs to update the list of env vars at https://github.com/blockscout/docs/blob/master/for-developers/information-and-settings/env-variables.md and I updated the version to master in the Version column. Changes will be reflected in this table: https://docs.blockscout.com/for-developers/information-and-settings/env-variables.
• If I add new indices into DB, I checked, that they are not redundant with PGHero or other tools

[coveralls]

Pull Request Test Coverage Report for Build 6d3d0a5531cb1276072272c06719a6f1661ef62f-PR-3622

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 37 unchanged lines in 3 files lost coverage.
• Overall coverage decreased (-1.7%) to 64.8%

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Files with Coverage Reduction	New Missed Lines	%
lib/block_scout_web/controllers/chain/market_history_chart_controller.ex	2	71.43%
lib/block_scout_web/checksum_address.ex	6	55.56%
lib/block_scout_web/views/smart_contract_view.ex	29	37.76%

Totals
Change from base Build c6d43e2d8e456e24dcf66078c0c9fc5699f25509:	-1.7%
Covered Lines:	2095
Relevant Lines:	3233

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💛 - Coveralls