Silence Clang static analyzer warnings

[giacomofiorin]

Fixes #581

[giacomofiorin]

@HubLot I fixed a couple where the purpose of the code may not be immediately evident. Can you get the Clang command used so that we can add it to the CI for this PR?

Easiest may be to add packages from Ubuntu (GH Actions) but we can also use the CentOS container.

[HubLot]

I added a new CI job for the Clang analyzer.
It took me some trials & errors but it works. I silent the warnings from lepton to avoid having it failing all the time. A log artifact can be also uploaded with the warnings only if they exists.

I fix some others warnings but it needs reviewing. Specially the one with the error_code not read. I found different ways of exiting a function inside the code so I tried to mimic one of them to fix the warnings.

[giacomofiorin]

Thanks! I'll look at this and merge if appropriate.

Sorry we don't have a uniform way to handle exit codes, we started adding them with the VMD integration (beginning ~2014 or so) but much of the code predates even that time.