Fixed a segfault on PyPy

Author: dahlia

sass.c

@@ -244,7 +244,7 @@ PySass_compile(PyObject *self, PyObject *args, PyObject *kwds)
     }
 
 finalize:
-    if (PySequence_Check(include_paths)) {
+    if (include_paths != NULL && PySequence_Check(include_paths)) {
         free(include_paths_v);
     }
     return result;