Bug description
With a tile extractor like

random_tiles_extractor = RandomTiler(
    tile_size=(500, 500),
    n_tiles=6,
    level = 0,
    seed=42,
    check_tissue=False, 
    prefix="random/", 
    suffix=".png")

And a Slide with dimensions < than 500x500, the Tiler get stuck

To Reproduce
Steps to reproduce the behavior:

1. Instantiate a Slide
2. instantiate a tiler extractor using a tile_size param > than the slide dimensions
3. call .extract(my_slide) method
4. See error

Expected behavior
In a case like this throw a meaningful User Error