Ensure loseContext exists before calling it

[archmoj]

@birkskyum Similar fix was necessary to get plotly.js working with virtual-webgl (v1).
See plotly/mapbox-gl-js@71e2cfc

This is for your brilliant pull request plotly/plotly.js#7015
if you could possibly test a build with make-baselines-virtual-webgl to see if it passes on CircleCI
or alternatively add the following script to the top of plotly.js devtools/test_dashboard/index.js and then npm start to test interactively.

<script src="https://unpkg.com/browse/virtual-webgl@1.0.6/src/virtual-webgl.js"></script>

Launch Checklist

• Confirm your changes do not include backports from Mapbox projects (unless with compliant license) - if you are not sure about this, please ask!
• Briefly describe the changes in this PR.
• Link to related issues.
• Include before/after visuals or gifs if this PR includes visual changes.
• Write tests for all new functionality.
• Document any changes to public APIs.
• Post benchmark scores.
• Add an entry to CHANGELOG.md under the ## main section.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.37%. Comparing base (d919ba3) to head (7cc8f68).
Report is 7 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4245      +/-   ##
==========================================
- Coverage   87.73%   87.37%   -0.36%     
==========================================
  Files         242      242              
  Lines       33081    33081              
  Branches     2160     2173      +13     
==========================================
- Hits        29023    28906     -117     
- Misses       3088     3182      +94     
- Partials      970      993      +23     

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[birkskyum]

Thanks for upstreaming it!

When i run npm run start and go to gl2d heatmap, it appear to work both w/o the script tag - what should I look for interactively? Seems like it's also getting blocked on localhost.

Either way, I think this change makes sense as it's more accurately guarding the function call.

[birkskyum]

Can you add a changelog entry like this:
- ⚠️ Ensure loseContext exists before calling it ([#4245](https://github.com/maplibre/maplibre-gl-js/pull/4245))

in the bugfix section here:

maplibre-gl-js/CHANGELOG.md

Line 20 in 760f9d1

- _...Add new stuff here..._