[gtk] gl renderer: A GdkGLTexture's context might be NULL

[Timm Bäder <baedert src gnome org>]

commit 6a69dc6e5d2eeef2a9343f0d289c15d5565d6269
Author: Timm Bäder <mail baedert org>
Date:   Mon May 20 09:33:55 2019 +0200

    gl renderer: A GdkGLTexture's context might be NULL
    
    gdk_gl_texture_download ought to still work, but we can't make a NULL
    context current obviously.

 gsk/gl/gskgldriver.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
---
diff --git a/gsk/gl/gskgldriver.c b/gsk/gl/gskgldriver.c
index dfccd315fc..4dd603b040 100644
--- a/gsk/gl/gskgldriver.c
+++ b/gsk/gl/gskgldriver.c
@@ -511,8 +511,11 @@ gsk_gl_driver_get_texture_for_texture (GskGLDriver *self,
         {
           /* In this case, we have to temporarily make the texture's context the current one,
            * download its data into our context and then create a texture from it. */
-          gdk_gl_context_make_current (texture_context);
+          if (texture_context)
+            gdk_gl_context_make_current (texture_context);
+
           surface = gdk_texture_download_surface (texture);
+
           gdk_gl_context_make_current (self->gl_context);
         }
       else