rtpjitterbuffer: Don't use stats timer on the timers queue

The timer passed to update_timers may be from the stats timer. At the
moment, we could endup rescheduling (reusing) that timer onto the normal
timer queue, unschedul it as if it was from the normal timer queue or
duplicate it into the stats timer queue again. This was protected before
as the with the fact the stats timer didn't have a valid idx.
28 jobs for jitterbuffer-timer-reschedule in 79 minutes and 3 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Preparation
passed #589445
gst indent

00:00:22

passed #589444
manifest

00:00:29

 
  Build
passed #589455
build cerbero android universal

00:13:45

passed #589456
build cerbero cross win32

00:12:23

passed #589457
build cerbero cross win64

00:13:01

passed #589454
build cerbero fedora x86_64

00:14:43

manual #589459
gst-ios-12.2 allowed to fail manual
build cerbero ios universal
passed #589458
gst-macos-10.14
build cerbero macos x86_64

00:11:42

passed #589450
build clang fedora x86_64

00:19:30

passed #589446
build fedora x86_64

00:18:35

passed #589453
docker windows 1607
build msys2

00:15:51

passed #589447
build nodebug fedora x86_64

00:06:21

passed #589448
build static fedora x86_64

00:41:29

passed #589449
build static nodebug fedora x86_64

00:06:09

passed #589451
docker windows 1607
build vs2017 amd64

00:10:25

passed #589452
docker windows 1607
build vs2017 x86

00:12:21

 
  Test
passed #589711
check fedora

00:04:13

passed #589461
integration testsuites fedora

00:40:50

passed #589463
valgrind bad

00:06:13

passed #589464
valgrind ges

00:11:42

passed #589970
valgrind good

00:14:00

failed #589460
check fedora

00:02:57

failed #589947
valgrind good

00:12:36

failed #589869
valgrind good

00:04:43

failed #589462
valgrind good

00:07:32

 
  Integrate
passed #589465
android universal examples

00:07:02

passed #589466
documentation

00:07:22

manual #589467
gst-ios-12.2 allowed to fail manual
ios universal examples