[polari] thumbnailer: Dispose cairo context

[Florian Müllner <fmuellner src gnome org>]

commit 90b3400e377c9314a24861bd26d94790eed6af11
Author: Florian Müllner <fmuellner gnome org>
Date:   Wed Dec 18 17:51:19 2019 +0100

    thumbnailer: Dispose cairo context

 src/thumbnailer.js | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/src/thumbnailer.js b/src/thumbnailer.js
index 8585468..2733213 100644
--- a/src/thumbnailer.js
+++ b/src/thumbnailer.js
@@ -185,6 +185,7 @@ class App {
             targetHeight / sourceHeight);
         cr.setSourceSurface(surface, 0, 0);
         cr.paint();
+        cr.$dispose();
 
         target.writeToPNG(this._filename);
     }