Issue #16847: Fixed improper use of _PyUnicode_CheckConsistency() in

non-pydebug builds. Several extension modules now compile cleanly when
assert()s are enabled in standard builds (-DDEBUG flag).

Modules/_json.c

@@ -246,7 +246,9 @@ ascii_escape_unicode(PyObject *pystr)
         }
     }
     output[chars++] = '"';
+#ifdef Py_DEBUG
     assert(_PyUnicode_CheckConsistency(rval, 1));
+#endif
     return rval;
 }