[BUG] External assets not reflected in get_asset_url

[karosc]

When serving assets from an external path by setting:

serve_locally=False
and
assets_external_path=<url to external asset folder>

css, js, and favicon assets are pulled from the external asset directory when the app is initialized, but if I try to use app.get_asset_url(<asset>) it still pulls the asset from the dash directory rather than the external directory.

Would developers be ammenable to a pull request altering the get_asset_url function to look more like below?

def get_asset_url(self, path):
    if self.config.assets_external_path:
        asset = get_asset_path(
            self.config.assets_external_path,
            path,
            self.config.assets_url_path.lstrip("/"),
        )
    else:
        asset = get_asset_path(
            self.config.requests_pathname_prefix,
           path,
            self.config.assets_url_path.lstrip("/"),
       )

    return asset

For reference get_asset_path is defined in _utils.py as:

def get_asset_path(requests_pathname, asset_path, asset_url_path):

    return "/".join(
        [
            # Only take the first part of the pathname
            requests_pathname.rstrip("/"),
            asset_url_path,
            asset_path,
        ]
    )

[alexcjohnson]

Nice find, would you like to make a PR to fix this oversight?