Fix ocean-fill NaN replacement crashing on dask-backed rasters

Use the already-computed numpy array (base_np) instead of copying
the raw raster data, which may be a dask array that doesn't support
boolean mask assignment.

Author: brendancol

rtxpy/engine.py

@@ -1598,7 +1598,7 @@ def __init__(self, raster, width: int = 800, height: int = 600,
                 new_data = self._base_raster.data.copy()
                 new_data[cp.asarray(ocean_fill)] = cp.nan
             else:
-                new_data = self._base_raster.data.copy()
+                new_data = base_np.copy()
                 new_data[ocean_fill] = np.nan
             self._base_raster = self._base_raster.copy(data=new_data)
             # Re-derive working raster from updated base