SDL: calling SDL_SetWindowSize inside fullscreen callback doesn't work

**Version of emscripten/emsdk:**
```
emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 3.1.51 (c0c2ca1314672a25699846b4663701bcb6f69cca)
clang version 18.0.0git (https://github.com/llvm/llvm-project f2464ca317bfeeedddb7cbdea3c2c8ec487890bb)
Target: wasm32-unknown-emscripten
Thread model: posix
InstalledDir: /home/eliasdaler/work/emsdk/upstream/bin
```

When I register a full screen callback via `emscripten_set_fullscreenchange_callback`, calling `SDL_SetWindowSize` inside of the callback doesn't work and makes the image disappear.

However, if I poll the full screen state in the main loop and change `SDL_SetWindowSize` on full screen change, everything works as expected.

Repro can be found here: https://github.com/eliasdaler/em_test/tree/em_bug

Build instructions:

```sh
git clone https://github.com/eliasdaler/em_test/
cd em_test/
git checkout em_bug
mkdir build && cd build
emcmake cmake ..
cmake --build .
emrun src/site/index.html
```

To get it working properly

1. Uncomment [this](https://github.com/eliasdaler/em_test/blob/48f43a0f5c99bedaec630d52b338cdfcc607e878/src/Game.cpp#L111C9-L111C82)
2. Comment out [this](https://github.com/eliasdaler/em_test/blob/48f43a0f5c99bedaec630d52b338cdfcc607e878/src/Game.cpp#L20)