Add width and height check for MujocoRenderer

[Beanpow]

Description

The width and height of OffScreenViewer cannot be None otherwise, it will cause the error. Adding a type check before creating the opengl_context could provide more information for debugging.

Fixes #1225

Type of change

Please delete options that are not relevant.

• Documentation only change (no code changed)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• I have run the pre-commit checks with pre-commit run --all-files (see CONTRIBUTING.md instructions to set it up)
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[Beanpow]

@Kallinteris-Andreas could you review this code?

[Kallinteris-Andreas]

will be merged after #1229

[Kallinteris-Andreas]

LGTM I will merge after #1229 , @Beanpow you may need to do a merge then,

[pseudo-rnd-thoughts]

@Kallinteris-Andreas are you sure we can't merge now?