Fix/handle-out-of-bounds-tiles

[cr3a7ure]

• Do not throw exception on tile fetch when response status is 400
• 400 on OpenStreetMaps and GeoServer means that you are out of bounds
• Thus allowing to count correctly the retrieved tiles and fire saveend

This is a common scenario when retrieving tiles beyond zoom level 19 on openstreetmaps and from other servers too.
I followed the least changes approach.
The saved blob, does not get rendered from leaflet. We can also return a null sized image blob.

Thanks for the time to review it.

[allartk]

Hi, thanks for the pull request!

I wonder, can you prevent those download attempts be configuring bounds and zooms of the layer?

[cr3a7ure]

I have not studied your code in more depth TBH, but I believe it will require more logic for sure.
Especially if you had in mind the base layer which covers most of the times the whole map.
I am serving custom geoTIFF overlays as WMTS layers which means that they are oddly shaped.
I cannot suggest a universal way to retrieve bounds/zoom/layer.

On my scenario, I retrieve the bounds of the layer via WMS Info calls on GeoServer, I set those in the extent of the leaflet map and then proceed to use saveTiles on those bounds.

For compatibility reasons and stability we could use a flag in options to allow those 400s be counted towards saveend event.
I have deployed the change and monitoring the user experience.

Thanks for jumping in.