Handle tile bound errors (as 404)

[drewbo]

Currently tile outside of bounds errors end up in the logs (making debugging more difficult) and as a 500 error (not the best user response). We can catch these and handle:

rio_tiler.errors.TileOutsideBounds: Tile 9/449/202 is outside image bounds

cc: @leothomas @vincentsarago

[vincentsarago]

Yeah we fixed this upstream by adding a middleware