Merge r62235 from trunk.

Fix zlib crash from zlib.decompressobj().flush(val) when val was not positive.
It tried to allocate negative or zero memory.  That fails.
diff --git a/Lib/test/test_zlib.py b/Lib/test/test_zlib.py
index 4440942..6b3b12e 100644
--- a/Lib/test/test_zlib.py
+++ b/Lib/test/test_zlib.py
@@ -71,6 +71,11 @@
         # verify failure on building decompress object with bad params
         self.assertRaises(ValueError, zlib.decompressobj, 0)
 
+    def test_decompressobj_badflush(self):
+        # verify failure on calling decompressobj.flush with bad params
+        self.assertRaises(ValueError, zlib.decompressobj().flush, 0)
+        self.assertRaises(ValueError, zlib.decompressobj().flush, -1)
+
 
 
 class CompressTestCase(unittest.TestCase):