zoomOffset and zoomReverse parameters aren't used

[vinicentus]

The parameters aren't used in any calculations. This means that if one tries to use 512px tiles with a zoomOffset of -1 (as suggested here under "Display map using Leaflet") it just won't work.

https://github.com/johnpryan/flutter_map/blob/a639b6d72fd69d7c4918e37cca0e12b79c4334eb/lib/src/layer/tile_layer.dart#L45-L46

[vinicentus]

I can confirm that this is now working. Thank you @maRci002 :)