Fix PlayMedia builtin for smart playlists and playlists

[DaveTBlake]

PlayMedia builtin is broken in v18 when called for a playlist or smart playlist that needs to be recursively expanded into actual media items e.g. a smart playlist of artist or albums. Reported in https://forum.kodi.tv/showthread.php?tid=344892

This regression was initially introduced by #11747 that ensured individual items are played with a playlist. It overlooked that item.IsVideo() returns true for .m3u and .xsp files and thus passed them to CPlayListPlayer::Play, which is unable to expand the .xsp file into the individual items to be queued, as if they were a single media file. Then #14183 attempted to fix the consequences - PlayMedia was not playing smart playlists and simple playlists are played as a single huge item. However this fix does not work for all smart playlists, they are not fully expanded and CPlayListPlayer::Play can not handle lists of artists or albums.

This fix restores the PlayMedia functionality for playlists and smartplaylists.

[DaveTBlake]

@notspiff said he trusted me.... All testing, no point letting this languish here

[Acidzero2020]

@DaveTBlake
After this change i have the follow problem:
When I play a *.strm file from the widget (e.g. last viewed), the player does not display any information, see pictures.

The *.strm file calls an addon which only starts a video e.g:
listitem = xbmcgui.ListItem()
listitem.setPath( "http://184.72.239.149/vod/smil:BigBuckBunny.smil/playlist.m3u8")
xbmcplugin.setResolvedUrl(pluginhandle, True, listitem)

start:

before commit:

after commit: