Allow to write to unexisting directory

`ifcopenshell.write("/unexisting/path/model.ifc")` was failing without
throwing an error. It now works and a test ensure it works.

src/ifcopenshell-python/test/test_write.py

@@ -61,3 +61,6 @@ class TestWrite:
 
     def test_write_anyextension_ifczip_ifcxml_format(self):
         self.assert_model_is_written("model.anyextension", format=".ifcXML", zipped=True)
+
+    def test_write_to_non_existing_dir(self):
+        self.assert_model_is_written("tmp/model.ifczip")