Convert the use of player_ctx in mythtranscode to QPointer<>

We have far too many places in the transcode code path that delete player_ctx
and return.  Unfortunately, freeing "transcode" also will try to delee
player_ctx, but it's already deleted, and not nulled out.  Rather than putting
many instances of "player_ctx = NULL", I opted to make PlayerContext a
QObject, and then just use QPointer<PlayerContext> as this will clear itself
to NULL as soon as it is destroyed.

Fixes #10616

mythtv/libs/libmythtv/playercontext.h

@@ -11,6 +11,7 @@ using namespace std;
 #include <QMutex>
 #include <QHash>
 #include <QRect>
+#include <QObject>
 #include "mythtvexp.h"
 #include "mythdeque.h"
 #include "tv.h"
@@ -42,8 +43,9 @@ typedef enum
 typedef deque<QString>         StringDeque;
 typedef QHash<QString,QString> InfoMap;
 
-class MTV_PUBLIC PlayerContext
+class MTV_PUBLIC PlayerContext : public QObject
 {
+    Q_OBJECT
   public:
     PlayerContext(const QString &inUseID = QString("Unknown"));
     ~PlayerContext();

mythtv/programs/mythtranscode/transcode.h

@@ -1,9 +1,10 @@
+#include <QPointer>
 #include "recordingprofile.h"
 #include "fifowriter.h"
 #include "transcodedefs.h"
 #include "programtypes.h"
+#include "playercontext.h"
 
-class PlayerContext;
 class ProgramInfo;
 class NuppelVideoRecorder;
 class MythPlayer;
@@ -49,7 +50,7 @@ class Transcode : public QObject
     int                     keyframedist;
     NuppelVideoRecorder    *nvr;
     MythPlayer             *player;
-    PlayerContext          *player_ctx;
+    QPointer<PlayerContext> player_ctx;
     RingBuffer             *inRingBuffer;
     RingBuffer             *outRingBuffer;
     FIFOWriter             *fifow;