tag: id3v2: fix frame size check and potential invalid reads

Check the right variable when checking if there's
enough data left to read the frame size.

Closes https://gitlab.freedesktop.org/gstreamer/gst-plugins-base/-/issues/876

Part-of: <gstreamer/gst-plugins-base!1066>
35 jobs for !1066 with backport-mr-1065-into-1.18-id3v2-parsing-fix-frame-size-check in 43 minutes and 4 seconds (queued for 5 seconds)
detached
Status Job ID Name Coverage
  Build Docker
passed #7995089
alpine amd64 manifest builder docker

00:00:27

passed #7995088
android docker

00:00:32

passed #7995086
cerbero fedora amd64 docker

00:00:31

passed #7995085
fedora amd64 docker

00:00:31

passed #7995090
gst-indent amd64 docker

00:00:31

 
  Preparation
passed #7995092
gst indent

00:00:09

passed #7995091
manifest

00:00:12

 
  Build
passed #7995101
gstreamer
build cerbero cross-android universal

00:09:39

passed #7995105
gst-ios-14.3
build cerbero cross-ios universal

00:25:11

passed #7997791
gstreamer
build cerbero cross win32

00:03:59

passed #7995103
gstreamer
build cerbero cross win64

00:04:25

passed #7995100
gstreamer
build cerbero fedora x86_64

00:04:33

passed #7995104
gst-macos-11.1
build cerbero macos x86_64

00:15:37

passed #7995096
build clang fedora x86_64

00:04:48

manual #7995099
docker windows 1809 allowed to fail manual
build msys2
passed #7995093
build nodebug fedora x86_64

00:04:39

passed #7995094
build static fedora x86_64

00:04:48

passed #7995095
build static nodebug fedora x86_64

00:04:31

passed #7995097
docker windows 1809
build vs2017 amd64

00:10:16

passed #7995098
docker windows 1809
build vs2017 x86

00:10:01

failed #7995102
gstreamer
build cerbero cross win32

00:03:31

 
  Test
passed #7997997
gstreamer
check fedora

00:04:49

passed #7995107
gstreamer
integration testsuites fedora 1/4

00:13:43

passed #7995108
gstreamer
integration testsuites fedora 2/4

00:15:55

passed #7995109
gstreamer
integration testsuites fedora 3/4

00:13:30

passed #7995110
gstreamer
integration testsuites fedora 4/4

00:15:15

passed #7995114
gstreamer
valgrind bad

00:05:03

passed #7995111
gstreamer
valgrind base

00:06:41

passed #7995115
gstreamer
valgrind ges

00:05:41

passed #7995112
gstreamer
valgrind good

00:08:50

passed #7995113
gstreamer
valgrind ugly

00:02:59

failed #7995106
gstreamer
check fedora

00:08:53

 
  Integrate
passed #7995116
cross-android universal examples

00:06:48

passed #7995118
gst-ios-14.3
cross-ios universal examples

00:03:47

passed #7995117
documentation

00:14:53