gl: Only unbind buffers/vertex attrib arrays if we can't directly bind the vertex array to 0

Binding the vertex array to 0 will unbind everything else already.

In the previous order older versions of the Intel GL driver caused
errors to be printed for every single call when disabling the vertex
attrib arrays after binding the vertex array to 0.
8 jobs for unbind-before-voa in 19 minutes and 24 seconds (queued for 10 seconds)
Status Job ID Name Coverage
  Preparation
passed #82444
gst indent

00:00:31

passed #82443
manifest

00:00:35

 
  Build
passed #82445
build fedora x86_64

00:03:22

 
  Test
passed #82446
check fedora

00:03:38

 
  Full Builds
passed #82447
build android arm64 api28

00:03:01

passed #82449
build cerbero cross win32

00:09:07

passed #82450
build cerbero cross win64

00:07:23

passed #82448
build cerbero fedora x86_64

00:07:46