Removing TileSource does not reset CRS

[katterfelto]

In my app I added to ability to select various background tile sources.

I also foolishly allowed the user to turn off the background tiles when this happens the CRS used in the control stays set to the tile CRS rather than reverting back to the original CRS defined in the Shapefile's.

I have a patch which records the original CRS prior to the TileSource being set and reverts the CRS if the TileSource is cleared