fix TextIOWrapper.read() when the buffer is not readable #5628
diff --git a/Lib/_pyio.py b/Lib/_pyio.py
index 654a69c..334c2b7 100644
--- a/Lib/_pyio.py
+++ b/Lib/_pyio.py
@@ -1696,6 +1696,7 @@
         return cookie
 
     def read(self, n=None):
+        self._checkReadable()
         if n is None:
             n = -1
         decoder = self._decoder or self._get_decoder()