Fixed -a flag for OpenGL rendering

[k4pran]

Overview: What does this pull request change?

Motivation and Explanation: Why and how do your changes improve the library?

Fixes #2009

When using the -a flag the opengl renderer was not outputting all scenes, this fixes it, but only made applicable to non-interactive mode.

Links to added or changed documentation pages

Further Information and Comments

Only tests for this exist for cairo, opengl tests will be added in #2008

Reviewer Checklist

• The PR title is descriptive enough for the changelog, and the PR is labeled correctly
• If applicable: newly added non-private functions and classes have a docstring including a short summary and a PARAMETERS section
• If applicable: newly added functions and classes are tested

[hydrobeam]

Tested out the changes and it does work 👍, so LGTM. I'm curious as to what these changes do and why it didn't work before, yet worked with cairo?

[k4pran]

Tested out the changes and it does work 👍, so LGTM. I'm curious as to what these changes do and why it didn't work before, yet worked with cairo?

The opengl scene selection has different logic to accommodate interactive mode, scene rerun etc so it is a bit more complex, there was an issue where opengl only ever rendered the first scene and ignored user selection, that was fixed but I guess the issue with -a was still broken. These changes basically just use similar logic to the Cairo one and ignore the rerun scene logic