Map thumbnails extent always cover the whole globe

[giohappy]

Expected Behavior

When a map is created the thumbnail covers the area of its map layers

Actual Behavior

When a map is created the thumbnail covers the whole globe.

For the creation of the thumbnail for a map, it cycles over the maps's maplayers. I suspect that at creation time we're generating the thumbnail before the maplayers are saved to DB. In fact, if you recreate the thumbnail afterward (with the thumbnail widget), the extent is calculated correctly.

Steps to Reproduce the Problem

1. Open a dataset that doesn't cover the whole globe
2. Click "Create map"
3. Save the map
4. The thumbnail covers the whole globe