Do not set "__path__" attribute on non-package modules.

Cython/Utility/ModuleSetupCode.c

@@ -944,11 +944,13 @@ static CYTHON_SMALL_CODE int __Pyx_check_single_interpreter(void) {
     return 0;
 }
 
-static CYTHON_SMALL_CODE int __Pyx_copy_spec_to_module(PyObject *spec, PyObject *moddict, const char* from_name, const char* to_name) {
+static CYTHON_SMALL_CODE int __Pyx_copy_spec_to_module(PyObject *spec, PyObject *moddict, const char* from_name, const char* to_name, int allow_none) {
     PyObject *value = PyObject_GetAttrString(spec, from_name);
     int result = 0;
     if (likely(value)) {
+        if (allow_none || value != Py_None) {
             result = PyDict_SetItemString(moddict, to_name, value);
+        }
         Py_DECREF(value);
     } else if (PyErr_ExceptionMatches(PyExc_AttributeError)) {
         PyErr_Clear();
@@ -978,10 +980,10 @@ static CYTHON_SMALL_CODE PyObject* ${pymodule_create_func_cname}(PyObject *spec,
     if (unlikely(!moddict)) goto bad;
     // moddict is a borrowed reference
 
-    if (unlikely(__Pyx_copy_spec_to_module(spec, moddict, "loader", "__loader__") < 0)) goto bad;
-    if (unlikely(__Pyx_copy_spec_to_module(spec, moddict, "origin", "__file__") < 0)) goto bad;
-    if (unlikely(__Pyx_copy_spec_to_module(spec, moddict, "parent", "__package__") < 0)) goto bad;
-    if (unlikely(__Pyx_copy_spec_to_module(spec, moddict, "submodule_search_locations", "__path__") < 0)) goto bad;
+    if (unlikely(__Pyx_copy_spec_to_module(spec, moddict, "loader", "__loader__", 1) < 0)) goto bad;
+    if (unlikely(__Pyx_copy_spec_to_module(spec, moddict, "origin", "__file__", 1) < 0)) goto bad;
+    if (unlikely(__Pyx_copy_spec_to_module(spec, moddict, "parent", "__package__", 1) < 0)) goto bad;
+    if (unlikely(__Pyx_copy_spec_to_module(spec, moddict, "submodule_search_locations", "__path__", 0) < 0)) goto bad;
 
     return module;
 bad: