Range is not applied to default colormap

[henhuy]

Default colormap (if not setting up a legend) is not working properly (no range attribute set). This leads to color artefacts like this:

This is related to code in https://github.com/geodesign/django-raster/blob/34fffe3d1f921b2850d3cad598a3c9b382e1fec7/raster/views.py#L82-L100 as range and entries are only added if colormap exists in the first place. After removing else and unindending range and entries part, raster layer looks as expected: