[C] report by Clang Static Analyzer

I used Clang Static Analyzer to detect potential issues with the client and got a report like the following:

Attached is the full report (unzip and open index.html in the browser).

scan-build-report.zip

We'll review and address these issues with separate PRs.

If anyone wants to help, please reply to let us know.

cc @zhemant (2018/11) @ityuhui (2019/12) @michelealbano (2020/03)