Fix TestIPTVRecorder after change to IPTVChannelInfo

[ijc]

My patches in ​https://code.mythtv.org/trac/ticket/13488 broke the related unit tests. My apologies.

Attached is the fix (also pushed to ​https://github.com/MythTV/mythtv/pull/184).

Commit message for reference:

    Fix TestIPTVRecorder after change to IPTVChannelInfo
    
    In a60e7429a09a ("IPTVChannelInfo: explictly set IPTVTuningData protocol to
    invalid") I removed `IPTVChannelInfo::IsValid()` thinking it was unused but
    missed the uses in these test cases. Reintroduce the method, but make it
    `protected` and a friend of the `TestIPTVRecorder` class.
    
    The above change also changed the behaviour of `IPTVChannelInfo`'s constructors
    such that the protocol is not always probed, and therefore `IsValid()` is not
    necessarily true. This is the case when constructed via
    `IPTVChannelFetcher::ParsePlayList`. Update `TestIPTVRecorder::ParseChanInfo` to
    reflect this by now asserting that the tuning data is not valid and that the
    protocol is `inValid` as expected.

[paul-h]

I'll commit this for now but I do want to store the protocol in the DB so we only have to do the test download once.

There are also some URL's we don't handle properly at all like this made up one since the URL doesn't end in .m3u8 :-

​http://example.com:1234/playlist.m3u8?id=YYYY

[paul-h]

In [changeset:"36d96c956969a85feb8578f0cbe2cc42fee01016/mythtv"

36d96c956/mythtv]:

(The changeset message doesn't reference this ticket)