Fix handle allocation

[cwfitzgerald]

Checklist

• CI Checked:
  • cargo fmt has been ran
  • [x]cargo clippy reports no issues
  • cargo test succeeds
  • cargo rend3-doc has no warnings
  • cargo deny check issues have been fixed or added to deny.toml
• Manually Checked:
  • relevant examples/test cases run
  • changes added to changelog
    • Add credit to yourself for each change: Added new functionality @githubname.

Related Issues

#533

Description

We were allocating handles before validating the resources given to us. This caused a drop instruction to get added even though an add instruction never happened.

[John-Nagle]

This is working. When I run an overly large scene, there is no crash, rendering of previously loaded content works fine, and new mesh creation attempts return the error ExceededMaximumBufferSize Thanks. I can work with this.

Now I have level-of-detail work to do on my side, to take appropriate action when full.