[gtk+] glarea: Avoid a crash

[Matthias Clasen <matthiasc src gnome org>]

commit 6ea827cde5b97d1681d269a8200c26189a4213bd
Author: Matthias Clasen <mclasen redhat com>
Date:   Wed Jan 17 19:48:33 2018 -0500

    glarea: Avoid a crash
    
    We must only delete the texture if it is not NULL.

 gtk/gtkglarea.c |    7 +++++--
 1 files changed, 5 insertions(+), 2 deletions(-)
---
diff --git a/gtk/gtkglarea.c b/gtk/gtkglarea.c
index efe4899..8e3cf4c 100644
--- a/gtk/gtkglarea.c
+++ b/gtk/gtkglarea.c
@@ -601,8 +601,11 @@ gtk_gl_area_delete_textures (GtkGLArea *area)
 {
   GtkGLAreaPrivate *priv = gtk_gl_area_get_instance_private (area);
 
-  delete_one_texture (priv->texture);
-  priv->texture = NULL;
+  if (priv->texture)
+    {
+      delete_one_texture (priv->texture);
+      priv->texture = NULL;
+    }
 
   /* FIXME: we need to explicitly release all outstanding
    * textures here, otherwise release_texture will get called