AV subtitles: fix redrawing issue and conflation with text zoom factor.

mythtv/libs/libmythtv/subtitlescreen.cpp

@@ -557,6 +557,7 @@ void SubtitleScreen::EnableSubtitles(int type, bool forced_only)
{
    if (forced_only)
    {
        SetElementDeleted();
        SetVisible(true);
        SetArea(MythRect());
        return;
@@ -576,18 +577,20 @@ void SubtitleScreen::EnableSubtitles(int type, bool forced_only)
    ClearAllSubtitles();
    SetVisible(m_subtitleType != kDisplayNone);
    SetArea(MythRect());
    m_textFontZoom  = gCoreContext->GetNumSetting("OSDCC708TextZoom", 100);
    switch (m_subtitleType)
    {
    case kDisplayTextSubtitle:
    case kDisplayRawTextSubtitle:
        m_family = kSubFamilyText;
        m_textFontZoom  = gCoreContext->GetNumSetting("OSDCC708TextZoom", 100);
        break;
    case kDisplayCC608:
        m_family = kSubFamily608;
        m_textFontZoom  = gCoreContext->GetNumSetting("OSDCC708TextZoom", 100);
        break;
    case kDisplayCC708:
        m_family = kSubFamily708;
        m_textFontZoom  = gCoreContext->GetNumSetting("OSDCC708TextZoom", 100);
        break;
    case kDisplayAVSubtitle:
        m_family = kSubFamilyAV;