Fix T45746: PNG UV layout export is blank with new depsgraph.

Looks like we need an explicit Scene.update() call here...

io_mesh_uv_layout/__init__.py

@@ -21,13 +21,12 @@
 bl_info = {
     "name": "UV Layout",
     "author": "Campbell Barton, Matt Ebb",
-    "version": (1, 1),
-    "blender": (2, 62, 0),
+    "version": (1, 1, 1),
+    "blender": (2, 75, 0),
     "location": "Image-Window > UVs > Export UV Layout",
     "description": "Export the UV layout as a 2D graphic",
     "warning": "",
-    "wiki_url": "http://wiki.blender.org/index.php/Extensions:2.6/Py/"
-                "Scripts/Import-Export/UV_Layout",
+    "wiki_url": "http://wiki.blender.org/index.php/Extensions:2.6/Py/Scripts/Import-Export/UV_Layout",
     "support": 'OFFICIAL',
     "category": "Import-Export",
 }

io_mesh_uv_layout/export_uv_png.py

@@ -131,6 +131,8 @@ def write(fw, mesh_source, image_width, image_height, opacity, face_iter_func):
     scene.render.image_settings.file_format = 'PNG'
     scene.render.filepath = filepath
 
+    scene.update()
+
     data_context = {"blend_data": bpy.context.blend_data, "scene": scene}
     bpy.ops.render.render(data_context, write_still=True)