meson: Always define gstgl_dep to a valid dependency object

Fixes configure error when gl support was auto-detected as not being
available:

ext/gl/meson.build:50:20: ERROR:  Unknown variable "gstgl_dep".

diff --git a/gst-libs/gst/gl/meson.build b/gst-libs/gst/gl/meson.build
index 8a5a83f..58bcb3d 100644 (file)
--- a/gst-libs/gst/gl/meson.build
+++ b/gst-libs/gst/gl/meson.build
@@ -829,4 +829,6 @@ if build_gstgl
 
 elif get_option('gl').enabled()
   error('GStreamer OpenGL integration required via options, but needed dependencies not found.')
+else
+  gstgl_dep = dependency('', required : false)
 endif