No option to download over non-roaming mobile networks

[taitsmith]

I suppose this is tangentially related to #1326 and can be rolled into a PR for that, or one of its own.

When attempting to download some media for the first time, users are presented with a choice of allowed network types, which currently consists of 'wifi only' and 'mobile data and roaming':

When the dialog is created here, setPositiveButton() is called twice which turns 'mobile data' to 'mobile data and roaming'. Changing one to setNeutralButton() (and swapping negative/positive for order) provides users all three options:

[Maxr1998]

That's definitely an oversight! You are welcome to create a pull request to fix that too 👍