fix potential bugs

Author: xuantengh

Objects/funcobject.c

@@ -162,7 +162,8 @@ PyFunction_NewWithQualName(PyObject *code, PyObject *globals, PyObject *qualname
     PyObject *consts = code_obj->co_consts;
     assert(PyTuple_Check(consts));
     PyObject *doc;
-    if (PyTuple_Size(consts) >= 1 && code_obj->co_flags & CO_HAS_DOCSTRING) {
+    if (code_obj->co_flags & CO_HAS_DOCSTRING) {
+        assert(PyTuple_Size(consts) >= 1);
         doc = PyTuple_GetItem(consts, 0);
         if (!PyUnicode_Check(doc)) {
             doc = Py_None;

Python/codegen.c

@@ -1233,9 +1233,9 @@ codegen_function_body(compiler *c, stmt_ty s, int is_async, Py_ssize_t funcflags
             return ERROR;
         }
         Py_ssize_t idx = _PyCompile_AddConst(c, docstring);
+        Py_XDECREF(docstring);
         RETURN_IF_ERROR_IN_SCOPE(c, idx < 0 ? ERROR : SUCCESS);
     }
-    Py_XDECREF(docstring);
 
     NEW_JUMP_TARGET_LABEL(c, start);
     USE_LABEL(c, start);