Fix St.ImageContent.set_bytes missing Cogl.Context argument

set_bytes() takes a Cogl.Context as its first parameter (added upstream
in GNOME Shell 48, see js/ui/screenshot.js); omitting it produced
"At least 6 arguments required, but only 5 passed" for every frame,
which fell through to the equally non-functional Clutter.Image fallback
and left the live wallpaper blank.

lib/liveWallpaper.js

@@ -15,13 +15,19 @@ import {loadGstreamerModules, GSTREAMER_INSTALL_HINT} from './gstreamerAvailabil
  * mechanism gnome-shell's own code uses for uploading raw pixel buffers —
  * is tried first, with the legacy Clutter.Image/set_data path kept only as
  * a fallback for older shells.
+ *
+ * St.ImageContent.set_bytes() takes a Cogl.Context as its first argument
+ * (see js/ui/screenshot.js upstream) — omitting it is what produced
+ * "At least 6 arguments required, but only 5 passed".
  */
 const FRAME_IMAGE_STRATEGIES = [
     {
         name: 'St.ImageContent',
         create: (width, height) => St.ImageContent.new_with_preferred_size(width, height),
         upload: (image, Cogl, data, width, height) =>
-            image.set_bytes(GLib.Bytes.new(data), Cogl.PixelFormat.RGBA_8888, width, height, width * 4),
+            image.set_bytes(
+                global.stage.context.get_backend().get_cogl_context(),
+                GLib.Bytes.new(data), Cogl.PixelFormat.RGBA_8888, width, height, width * 4),
     },
     {
         name: 'Clutter.Image',