Fix typo in unicode_decode_call_errorhandler_writer()

Bug introduced by changeset 7ed9993d53b4.
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index c4157d8..d4cb9c9 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -4124,7 +4124,7 @@
     if (PyUnicode_GET_LENGTH(repunicode) > 1)
         writer->overallocate = 1;
     if (_PyUnicodeWriter_WriteStr(writer, repunicode) == -1)
-        return
+        goto onError;
 
     *endinpos = newpos;
     *inptr = *input + newpos;