Fixed a corner case that I've witnessed, but cannot reproduce.

lib/cartopy/mpl/patch.py

@@ -206,7 +206,7 @@ def path_to_geos(path, force_ccw=False):
                 isinstance(geom, Polygon) and
                 collection[-1][0].contains(geom.exterior)):
             collection[-1][1].append(geom.exterior)
-        else:
+        elif not geom.is_empty:
             collection.append((geom, []))
 
     # Convert each (external_geom, [internal_polygons]) pair into a