rtpjitterbuffer: Clear clock master before unreffing

Make sure to clear any master clock on the media_clock
before unreffing it to release the timer callback that's
updating the clock and keeping it reffed.
19 jobs for rtpjitterbuffer-clear-clock-master in 94 minutes and 38 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Preparation
passed #360698
gst indent

00:00:29

passed #360697
manifest

00:00:41

 
  Build
passed #360704
build cerbero android universal

00:11:28

passed #360705
build cerbero cross win32

00:08:54

passed #360706
build cerbero cross win64

00:06:04

passed #360703
build cerbero fedora x86_64

00:05:43

passed #360708
gst-ios-12.2
build cerbero ios universal

00:42:25

passed #360707
gst-macos-10.14
build cerbero macos x86_64

00:10:53

passed #360699
build fedora x86_64

00:07:35

passed #360700
build nodebug fedora x86_64

00:06:06

passed #360701
build static fedora x86_64

00:14:21

passed #360702
build static nodebug fedora x86_64

00:11:17

 
  Test
passed #360709
check fedora

00:03:46

passed #360710
integration testsuites fedora

00:07:52

passed #360712
valgrind bad

00:05:12

passed #360713
valgrind ges

00:03:27

passed #360711
valgrind good

00:18:26

 
  Integrate
passed #360714
android universal examples

00:07:49

passed #360715
documentation

00:04:11