tweak for early exit

Author: cmaloney

Lib/_pyio.py

@@ -1695,19 +1695,20 @@ def readall(self):
     def readinto(self, b):
         """Same as RawIOBase.readinto()."""
         m = memoryview(b).cast('B')
-        if hasattr(os, 'readv'):
-            self._checkClosed()
-            self._checkReadable()
-            try:
-                return os.readv(self._fd, (m, ))
-            except BlockingIOError:
-                return None
-        else:
+        if not hasattr(os, 'readv'):
             data = self.read(len(m))
             n = len(data)
             m[:n] = data
             return n
 
+        self._checkClosed()
+        self._checkReadable()
+        try:
+            return os.readv(self._fd, (m, ))
+        except BlockingIOError:
+            return None
+
+
     def write(self, b):
         """Write bytes b to file, return number written.