[0.17.74] dirt overlaps with water

[Eiermann]

probably a minor bug: under some circumstances the dirt-effect overlaps with water. I can reproduce the issue with the following map-exchange string:

>>>eNpjYBBkcGVgZACCBnsQ5mBJzk/MgfAOOIAwV3J+QUFqkW5+U
SqyMGdyUWlKqm5+Jqri1LzU3ErdpMTiVJiJYFMzi/Lz0E1gLS7Jz
0MVKSlKTS1G1shdWpSYl1mai6QXoprR5t2s2Q0tcgwg/L+eQeH/f
xAGsh4A/QLCDFBPMQLFoIBFIjk/r6QoP0e3OLWkJDMv3SqxtMIqK
TOxmMNAz9QABDSwqUgrSi0sTc1LrrTKLc0pySzIyUwt4jDTA2swk
EXXkZufWVxSWpSKarAuTmV4TWdNzslMS2NgUHBkYChwBnmCkZGxW
mSd+8OqKfaMEG/pOUAZH6AiB5JgIp4whp8DTikVGMMEyRxjMPiMx
IBYWgK0AqqKwwHBgEi2gCQZGXvfbl3w/dgFO8Y/Kz9e8k1KsGc0d
BV598FonR1Qkh3kBSY4MWsmCOyEeYUBZuYDe6jUTXvGs2dA4I09I
ytIhwiIcLAAEge8mRkYBfiArAU9QEJBhgHmNDuYMSIOjGlg8A3mk
8cwxmV7dH8AA8IGZLgciDgBIsAWwl3GCGVGOkAkJBGyQK1GDMjWp
yA8dxJm42Ekq9HcgBkHyF5AE1FBCngukD0pcOIFM9wRwBC8wA7jO
cx3YGZAgA/2DEv4Gw8AACqb3z0=<<<

You will find the overlap at the following position (just walk straight upwards): 85, -635

[posila]

Thank you for taking the time to post bug report.

It indeed minor issue. Thanks for the map exchange string, if we ever get around to fixing this, it will be helpful.