setStyle's transformStyle: handle a possibility of map being initialized without a style

[ambientlight]

Fixes the exception that would be thrown in

maplibre-gl-js/src/ui/map.ts

Line 1489 in 9e31559

if (options.transformStyle && !this.style._loaded) {

when map.setStyle is passed with transformStyle option and map is initialized without an initial style.

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.
• Write tests for all new functionality.
• Manually test the debug page.
• Add an entry to CHANGELOG.md under the ## main section.

[github-actions]

Bundle size report:

Size Change: -4 B
Total Size Before: 206 kB
Total Size After: 206 kB

Output file	Before	After	Change
maplibre-gl.js	197 kB	197 kB	-4 B
maplibre-gl.css	9.09 kB	9.09 kB	0 B

ℹ️ View Details

No major changes

[HarelM]

Please add changelog and a test for the map load event.