scan-build cleanup + allocation fail handling

[Ongy]

This is based on https://github.com/emersion/mako/pull/228

First commit unique to this PR cleans up 3 possible memory leask detected via scan-build.

Second commit sprinkles couple of allocation failure handlers into the code. Though I don't think there's a system with a reasonable use for mako that doesn't use overcommit and actualy allows to have an allocation failure.

[vilhalmer]

This has a bunch of extra commits from your other PR.

[vilhalmer]

(It occurs to me I don't actually know if github allows you to represent a PR based on another…)

[emersion]

Converted to a draft to make it clear this shouldn't be merged before #228

[Ongy]

Not really. Github allows to have PRs into PRs, but that's then not tracked on the main repo.

I don't think there's a built-in feature for PR based on PR. Draft sounds good :)

[emersion]

Needs rebase

[Ongy]

There's still a couple of strdup() and maybe some of the pango functions left out. If we also want to check them, I'll add them as well, but I feel like this makes things considerably harder to read, witch questionabe value (non-overcommit systems with graphics are rare these days).

[emersion]

Closing because this is too old/outdated. Please re-open a new PR if you want to work on this again!