Fix map staying blank until moved (#2217)

If the style arrives before the map's initial `style.load`,
`componentDidUpdate` skips `setStyle` because `state.map` is still null.
The `setState` on `style.load` is then blocked by
`shouldComponentUpdate`, because `JSON.stringify` throws on the MapLibre
`Map` in state, so the style is only applied after a later prop change,
e.g. moving the map.

Fix: `shouldComponentUpdate` compares state fields by reference instead
of stringifying them. `zoom` is excluded: it changes on every zoom frame
but is only read when a layer popup opens.

## Launch Checklist

 - [x] 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.~~ (removed per review)
 - [x] Add an entry to `CHANGELOG.md` under the `## main` section.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

https://claude.ai/code/session_01WDkBFXcoMv8K4QSHA6P3Fg


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_Generated by [Claude Code](https://claude.ai/code)_

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Co-authored-by: Claude <noreply@anthropic.com>

CHANGELOG.md

@@ -17,6 +17,7 @@
 - The map's data listener now fires on tile loads again, so source and vector layer field autocompletion is populated
 - The `maputnik` desktop binary now opens the default browser automatically on startup (opt out with `--no-browser`)
 - Keyboard shortcuts now keep working while the map has focus, instead of going dead until the map is blurred
+- The map no longer stays blank on load until it is moved, when the style loads before the map is ready
 - _...Add new stuff here..._
 
 ## 3.1.0

src/components/MapMaplibreGl.tsx

@@ -107,7 +107,7 @@ class MapMaplibreGlInternal extends React.Component<MapMaplibreGlInternalProps,
   shouldComponentUpdate(nextProps: MapMaplibreGlInternalProps, nextState: MapMaplibreGlState) {
     let should = false;
     try {
-      should = JSON.stringify(this.props) !== JSON.stringify(nextProps) || JSON.stringify(this.state) !== JSON.stringify(nextState);
+      should = JSON.stringify(this.props) !== JSON.stringify(nextProps) || (Object.keys(nextState) as (keyof MapMaplibreGlState)[]).some(key => key !== "zoom" && this.state[key] !== nextState[key]);
     } catch(_e) {
       // no biggie, carry on
     }