[WEB] chrome mobile loses focus after SDL_ShowMessageBox

[ITotalJustice]

to reproduce:

1. open emu in chrome mobile
2. press loadstate
3. notice the error because it failed to loadstate (expected)
4. press okay on the alert
5. em now fires EMSCRIPTEN_EVENT_BLUR, sdl gets it and now fires SDL_WINDOWEVENT_FOCUS_LOST.
6. focus is never returned.

i think it only happens in chrome mobile. it works on firefox and safari ios, as well as desktop and desktop browsers.

haven't looked into how emscripten decides to fire a focus event yet. will need to find a fix and pr it.

useful links:

• SDL_ShowMessageBox does a simple js alert https://github.com/libsdl-org/SDL/blob/00452e47fa022314b4c21af2d4e5b63a53f89b8f/src/video/SDL_video.c#L4591

• sdl basically wraps around emscripten html wapper api https://github.com/libsdl-org/SDL/blob/10e1ef00e29479f3ac0ba4d0bf3e0083fca8b2a0/src/video/emscripten/SDL_emscriptenevents.c#L442.

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note related to the issue, but the variable name for the event data is wrong, copy and paste error https://github.com/libsdl-org/SDL/blob/10e1ef00e29479f3ac0ba4d0bf3e0083fca8b2a0/src/video/emscripten/SDL_emscriptenevents.c#L432