Fixed edge-lines and side rendering for snow layers

[buscher]

Fix "dirty" snow, because of wrong edge-lines and missing texture side darkening.

Pretty hard so see in game, but for comparison, In-Game:

Current master (without the fix):

With the fix:

[generrosity]

Applogies for the query, but wondering @buscher if part of the the 'edges' you fixing was these other visual gaps and alignments? Althought at a tight zoom of your fix, I suspect it is unrelated and I can log a new Issue for it

[buscher]

I can see the issues you are talking about. But yes, I did not touch this part of the code.
I will have to touch this code part again after adding powder_snow, then maybe I will look deeper into it and see if I can fix it, but this will have to come laaaaaaater, got lots of other stuff on my TODO list first :)