gldebug: make sure debug is initialized when calling gst_gl_insert_debug_marker

Usually gl debug is initialized in gst_gl_context_create_thread.
But this function is not used when using the GstGLContextGPUProcess
from ChromiumGStreamerBackend.

Received signal 11 SEGV_MAPERR 000000000000
gst_debug_category_get_threshold
gst_gl_insert_debug_marker
gst_gl_base_filter_gl_start

gst-libs/gst/gl/gstgldebug.c

@@ -333,6 +333,8 @@ gst_gl_insert_debug_marker (GstGLContext * context, const gchar * format, ...)
   gint len;
   va_list args;
 
+  _init_debug ();
+
   /* are we enabled */
   if (gst_debug_category_get_threshold (gst_gl_marker_debug) < GST_LEVEL_FIXME)
     return;