Fix test_decodeescape()

Author: vstinner

Objects/bytesobject.c

@@ -3774,6 +3774,11 @@ byteswriter_create(Py_ssize_t size, int use_bytearray)
 
     if (size >= 1) {
         if (byteswriter_resize(writer, size, 0) < 0) {
+#ifdef Py_DEBUG
+            // Write the canary byte so byteswriter_check_canary_byte()
+            // doesn't fail in PyBytesWriter_Discard()
+            byteswriter_write_canary_byte(writer);
+#endif
             PyBytesWriter_Discard(writer);
             return NULL;
         }