[#4340] Fixes possible access to undefined object

[birdofpreyru]

Fixes regression in the latest v4.5.0 release —
Fixes #4340.

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

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 87.79%. Comparing base (4b98e75) to head (efb08cf).
Report is 5 commits behind head on main.

Files	Patch %	Lines
src/render/painter.ts	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4431      +/-   ##
==========================================
+ Coverage   87.57%   87.79%   +0.22%     
==========================================
  Files         246      246              
  Lines       33396    33396              
  Branches     2223     2184      -39     
==========================================
+ Hits        29247    29321      +74     
+ Misses       3130     3076      -54     
+ Partials     1019      999      -20     

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[HarelM]

Any chance you could create a unit test to cover this scenario?

[birdofpreyru]

@HarelM I have added the test.

I also got a better idea, why the problem happened — when a new Style instance is set on the map, the painter's render() method might be called before the style's asynchronous loadURL() operation completes, and the stylesheet value is attached to the style only when loadURL() completes, inside the _load() method it calls.

It makes me think, perhaps there is a larger problem, and in the perfect world, something should be synchronized better, so that the style is not set on the map before the style is loaded, or render() is not called before the map style is loaded... but regardless, my PR hotfixes the problem with library crashing.

[HarelM]

THANKS