Our `IconDownloader` extended `BaseImageDownloader` from UIL. There was an
explicit check in the F-Droid `IconDownloader` which looks for
HTTP/HTTPS/Bluetooth schemes. If it wasn't one of these, it fell back
to the base class. This was what was happening for local cached image
files. As such, when the `getInputStream(...)` method was refactored
to only use F-Droids `DownloadFactory` and not delegate to the base class,
it failed on local "file://" URLs.
This change introduces a `LocalFileDownloader` and makes the `DownloaderFactory`
aware of it.
The `BaseImageDownloader` class only provides support for the following schemes:
* HTTP
* HTTPS
* File
* Android content providers
* Android assets
* Android drawables
F-Droid now supports HTTP, HTTPS, and File URLs. There is not currently any
need for content proiders, assets or drawables to get icons for apps in F-Droid.
If there is a need in the future (e.g. an issue currently discusses loading
icons from installed apps if possible) then that specific `Downloader` can get
introduced to solve the problem.
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