vulkan: Fix build on Windows

gstvkwindow_win32.c(166): error C2065: 'msg_source': undeclared identifier
23 jobs for master in 47 minutes and 30 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Preparation
passed #912716
gst indent

00:00:41

passed #912715
manifest

00:00:26

 
  Build
passed #912726
build cerbero cross-android universal

00:08:27

manual #912730
gst-ios-12.2 allowed to fail manual
build cerbero cross-ios universal
passed #912727
build cerbero cross win32

00:05:32

passed #912728
build cerbero cross win64

00:04:40

passed #912725
build cerbero fedora x86_64

00:06:10

passed #912729
gst-macos-10.14
build cerbero macos x86_64

00:06:17

passed #912721
build clang fedora x86_64

00:05:53

passed #912717
build fedora x86_64

00:05:34

passed #912724
docker windows 1607
build msys2

00:12:03

passed #912718
build nodebug fedora x86_64

00:04:10

passed #912719
build static fedora x86_64

00:09:51

passed #912720
build static nodebug fedora x86_64

00:04:31

passed #912785
docker windows 1607
build vs2017 amd64

00:10:22

passed #912723
docker windows 1607
build vs2017 x86

00:10:09

failed #912784
docker windows 1607
build vs2017 amd64

00:00:10

failed #912722
docker windows 1607
build vs2017 amd64

00:00:07

 
  Test
failed #912731
gstreamer
check fedora

00:03:39

passed #912732
gstreamer
integration testsuites fedora

00:41:26

 
  Integrate
passed #912733
cross-android universal examples

00:07:13

skipped #912735
gst-ios-12.2 allowed to fail manual
cross-ios universal examples
passed #912734
documentation

00:02:12

 
Name Stage Failure
failed
check fedora Test
!! Could not derive your terminal width !!
Uploading artifacts...
gst-build/build/meson-logs/: found 2 matching files
validate-logs: found 3582 matching files

Uploading artifacts to coordinator... ok
id=912731 responseStatus=201 Created token=HZU23DYe
Uploading artifacts...
validate-logs/*.xml: found 1 matching files

Uploading artifacts to coordinator... ok
id=912731 responseStatus=201 Created token=HZU23DYe
ERROR: Job failed: exit code 1