raise an ValueError in getvalue() on closed StringIO (closes #12161)

Thanks for Catalin Iacob for the patch.
diff --git a/Misc/ACKS b/Misc/ACKS
index 164473f..0066b32 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -382,6 +382,7 @@
 Jeremy Hylton
 Gerhard Häring
 Fredrik Håård
+Catalin Iacob
 Mihai Ibanescu
 Lars Immisch
 Bobby Impollonia