MythMusic: don't use cdio_paranoia for CD playback

There is problem with cdio_paranoia_read_limited() getting stuck in a loop if
the CD is ejected while playing. In theory it should give up after a set
number of retries but that doesn't seem to be working in the latest version.

I tried to lock the CD tray while playing but while the media monitor supports
locking it doesn't appear to be working :( so the easiest solution for now is
to use the non paranoia cdio routines which do detect an ejected CD properly.
Silence a coverity warning about comparing the address of pointer 'child' when it might be null. None issue, but it does no harm to fix.
Initialise all members of MythUIFileBrowser which require initialisation. Coverity.
Initialise members of BrowserApi. Coverity.
Initialise float m_relativeSize() in the constructor. Value chosen is extremely arbitrary. Coverity.
Initialise callbacks in MythUIHelperPrivate constructor. It was done anyway a few moments later. Coverity
Check return value of FindThemeFile() when loading an image.
It is redundant to call indexIn() after exactMatch() for QRegExp, as exactMatch() will also populate capturedTexts(). Coverity (indirectly)
Initialise m_pixelAspectRatio in DisplayRes. Coverity.
Media Monitor: tell all handlers when a device status changes to MEDIASTAT_OPEN

This changes the media monitor to tell all handlers when a devices status
changes to MEDIASTAT_OPEN even if that handler doesn't support the current
media type.

This is necessary because the media type sometimes changes to MEDIATYPE_UNKNOWN
when a CD is ejected for example so the music media handler never gets to know
the CD has been ejected because it is only set to handle MEDIATYPE_AUDIO.
Merge remote-tracking branch 'upstream/master'