gloverlaycompositor: fix crash if buffer doesn't have video meta

Fix #501
19 jobs for overlay-crash in 60 minutes and 40 seconds (queued for 1 second)
Status Job ID Name Coverage
  Preparation
passed #298207
gst indent

00:00:36

passed #298206
manifest

00:00:38

 
  Build
passed #298208
build fedora x86_64

00:05:02

passed #298234
build nodebug fedora x86_64

00:05:23

failed #298209
build nodebug fedora x86_64

00:03:34

 
  Test
passed #298210
check fedora

00:02:55

passed #298211
integration testsuites fedora

00:07:03

 
  Full Builds
passed #298213
build cerbero android universal

00:10:45

passed #298214
build cerbero cross win32

00:05:59

passed #298215
build cerbero cross win64

00:03:45

passed #298212
build cerbero fedora x86_64

00:06:03

 
  Full Tests
passed #298219
valgrind bad

00:14:08

passed #298216
valgrind base

00:17:25

passed #298220
valgrind ges

00:05:30

passed #298368
valgrind good

00:06:46

passed #298218
valgrind ugly

00:02:50

failed #298342
valgrind good

00:08:00

failed #298217
valgrind good

00:18:48

 
  Apps
passed #298221
android universal examples

00:07:34