html5: when a browser can't find the music asset it needs, trace an error message and continue instead of crashing

[TerryCavanagh]

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[TerryCavanagh]

Oh, looks like this would require overwriting the lime preloader? Maybe it's time I did that anyway. Ok! https://github.com/TerryCavanagh/haxegon/issues/92

[TerryCavanagh]

This one's pretty complicated, it turns out.

Openfl secretly renames assets when loading them on different browsers - so if you have code to load a .ogg file on Microsoft Edge, for example - Edge will actually try to load an mp3 file. If the mp3 version is there, then great! If not, it'll crash - and worse than that, it'll crash and tell you that it's because it can't find the .ogg file.

Fixing this properly is going to involve some openfl pull requests, I think.