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 Name Job ID Coverage
  Preparation
passed gst indent #82444

00:00:31

passed manifest #82443

00:00:35

 
  Build
passed build fedora x86_64 #82445

00:03:22

 
  Test
passed check fedora #82446

00:03:38

 
  Full Builds
passed build android arm64 api28 #82447

00:03:01

passed build cerbero cross win32 #82449

00:09:07

passed build cerbero cross win64 #82450

00:07:23

passed build cerbero fedora x86_64 #82448

00:07:46