Commit 10a6889 (Fix segfault after music scan completes) causes SEGV on exit

[Lawrence Rust <lvr@…>]

Commit 10a6889 (Fix segfault after music scan completes) causes the FE to throw a SEGV whenever it exits.

Program terminated with signal 11, Segmentation fault.
#0  0xb2af898f in QMutex::lock (this=0xa04ca28) at thread/qmutex.cpp:151
151	    if (d->recursive) {
(gdb) bt
#0  0xb2af898f in QMutex::lock (this=0xa04ca28) at thread/qmutex.cpp:151
#1  0xb2afd9db in QMutexLocker (this=0x9dea8e0, time=4294967295)
    at ../../include/QtCore/../../src/corelib/thread/qmutex.h:102
#2  QThread::wait (this=0x9dea8e0, time=4294967295)
    at thread/qthread_unix.cpp:641
#3  0xa8038311 in MusicPlayer::stop (this=0x9f6d420, stopAll=true)
    at musicplayer.cpp:289
#4  0xa8037155 in MusicPlayer::~MusicPlayer (this=0x9f6d420, 
    __in_chrg=<value optimised out>) at musicplayer.cpp:115
#5  0xa80377cf in MusicPlayer::~MusicPlayer (this=0x9f6d420, 
    __in_chrg=<value optimised out>) at musicplayer.cpp:150
#6  0xa7fb4370 in mythplugin_destroy () at main.cpp:672
#7  0xb59f83a1 in MythPlugin::destroy (this=0x9f4aa78) at mythplugin.cpp:105
#8  0xb59f973c in MythPluginManager::DestroyAllPlugins (this=0x9cb63a8)
    at mythplugin.cpp:311
#9  0x08091eeb in main (argc=4, argv=0xbfeb9094) at main.cpp:1771
(gdb) print d
$1 = (QMutexPrivate *) 0x78006f
(gdb) print d->recursive
Cannot access memory at address 0x78006f

[Stuart Morgan <smorgan@…>]

In de851dd273eaa80689a427f915c7db40d015e0ba/mythtv:

Set m_cdWatcher to NULL after deletion, fixes segfault on exiting frontend. Fixes #10936

[Stuart Morgan <smorgan@…>]

In 9e0d839be7667056dc65b79711dda84159a1b13d/mythtv:

Set m_cdWatcher to NULL after deletion, fixes segfault on exiting frontend. Fixes #10936
(cherry picked from commit de851dd273eaa80689a427f915c7db40d015e0ba)