update git_layer_function to take xarray

Author: browniea

mhkit/river/io/d3d.py

@@ -224,6 +224,14 @@ def get_layer_data(
     if isinstance(var[0][0], np.ma.core.MaskedArray):
         max_layer = len(var[0][0])
 
+        if abs(layer_index) > max_layer:
+            raise ValueError(f"layer_index must be less than the max layer {max_layer}")
+
+        v = np.ma.getdata(var[time_index, :, layer_index], False)
+        dimensions = 3
+    elif isinstance(var[0][0], xr.core.variable.Variable):
+        max_layer = var[0][0].shape[0]
+
         if abs(layer_index) > max_layer:
             raise ValueError(f"layer_index must be less than the max layer {max_layer}")