Fix memory leaks in Jam Recorder

[softins]

Fixes #1019

EDIT: fixes leaks in the recorder, but there appear still to be others.

[genesisproject2020]

I've compiled the updated code and put it live on Swedish Open Jam 1 and 2. Now just waiting to see what's happens.

[hoffie]

Looks good to me! I can confirm that the following leaks no longer appear in valgrind after this PR. I therefore suggest merging this and continue leak hunting afterwards. :)

==129778==    by 0x1AD536: recorder::CJamClient::CJamClient(long long, int, QString, CHostAddress, QDir) (in /home/christian/Projects/jamulus/Jamulus)
==129778==    by 0x1AEAB7: recorder::CJamSession::Frame(int, QString, CHostAddress, int, CVector<short>, int) (in /home/christian/Projects/jamulus/Jamulus)
==129778==    by 0x1B18C6: recorder::CJamRecorder::OnFrame(int, QString, CHostAddress, int, CVector<short>) (in /home/christian/Projects/jamulus/Jamulus)

==129778== 438 (88 direct, 350 indirect) bytes in 1 blocks are definitely lost in loss record 120 of 165
==129778==    at 0x483ADEF: operator new(unsigned long) (vg_replace_malloc.c:342)
==129778==    by 0x5AF54E5: QObject::QObject(QObject*) (in /usr/lib/libQt5Core.so.5.15.2)
==129778==    by 0x1ADF21: recorder::CJamSession::DisconnectClient(int) (in /home/christian/Projects/jamulus/Jamulus)
==129778==    by 0x1AE1A8: recorder::CJamRecorder::OnDisconnected(int) (in /home/christian/Projects/jamulus/Jamulus)

==129778== 876 (112 direct, 764 indirect) bytes in 2 blocks are definitely lost in loss record 129 of 165
==129778==    at 0x483ADEF: operator new(unsigned long) (vg_replace_malloc.c:342)
==129778==    by 0x1ADF14: recorder::CJamSession::DisconnectClient(int) (in /home/christian/Projects/jamulus/Jamulus)
==129778==    by 0x1AE1A8: recorder::CJamRecorder::OnDisconnected(int) (in /home/christian/Projects/jamulus/Jamulus)
==129778==    by 0x5AEC581: QObject::event(QEvent*) (in /usr/lib/libQt5Core.so.5.15.2)

==129778== 1,744 (352 direct, 1,392 indirect) bytes in 4 blocks are definitely lost in loss record 146 of 165
==129778==    at 0x483ADEF: operator new(unsigned long) (vg_replace_malloc.c:342)
==129778==    by 0x5AF54E5: QObject::QObject(QObject*) (in /usr/lib/libQt5Core.so.5.15.2)
==129778==    by 0x1ADF21: recorder::CJamSession::DisconnectClient(int) (in /home/christian/Projects/jamulus/Jamulus)
==129778==    by 0x1AE1A8: recorder::CJamRecorder::OnDisconnected(int) (in /home/christian/Projects/jamulus/Jamulus)

[pljones]

Just so I don't get so nervous reading this, can it be a clearer comment, please:
// We have a reference to a CJamRecorder instance that should now have finished. Clean up the instance.
(pJamRecorder->moveToThread ( pthJamRecorder ); puts pJamRecorder into the thread and the pthJamRecorder ->wait() above - if we had one - waited for it to finish.)