Allowing setting coastline_approximation_precision=0 when using custom landmask

Author: Manuel Aghito

opendrift/models/basemodel/__init__.py

@@ -393,7 +393,7 @@ def __init__(self,
             'general:coastline_approximation_precision': {
                 'type': 'float',
                 'default': 0.001,
-                'min': 0.0001,
+                'min': 0.,
                 'max': 0.005,
                 'units': 'degrees',
                 'description': 'The precision of the particle position approximation to the coastline.',