S4.3: Some errors were detected yet a 0 code was returned

Created by: diegoherranz

Issue found on https://github.com/KiCad/kicad-symbols/issues/1114

errorExtra() doesn't mean non-zero return code unless preceded by an error(). So, a few errorExtra() calls now using error() instead.

I've also added a second commit with some code style fixes. Let me know if you disagree with any of that and I can change or remove it. Edit: I've removed that second commit and moved the style fixes to a different PR (https://github.com/KiCad/kicad-library-utils/pull/269) since they are separate things. It also includes fixes on many other files now.

Thanks!