V8: assetsService.load doesn't load any assets missing an expected file extension so promise never returns

assetsService.load doesn’t load any assets missing an expected file extension (anything other than js or css) and the promise never returns.

I’ve marked the issue as V8 but it also exists in late V7.

Reproduction

Steps

Try to load any assets without a file extension, for example:

assetsService
    .load(["https://www.bing.com/api/maps/mapcontrol?branch=release"])
    .then(onAssetsLoad, onAssetsError);

Specifics

Looks like it was broken by this change to add support for loading CSS and JS (instead of just JS): https://github.com/umbraco/Umbraco-CMS/commit/50f8f185031593c2f89f6c98eb2abf347da5c4b5#diff-ca9e001eb1d67c6dccdfdd7aeff07f77

Expected result

I would probably expect the function to assume any unmarked assets were JS and load them accordingly. I would also accept some kind of descriptive error.

Actual result

The load method doesn’t load the asset and the promise never returns.

[harry-gordon]

I finally have an afternoon put aside to work on this, you should receive my first Umbraco contib later today 🤞.

[nul800sebastiaan]

Fixed in https://github.com/umbraco/Umbraco-CMS/pull/6713