Merge pull request from GHSA-7hmr-442f-qc8j

The unit allocated for decNumberCompare was accidentally removed by
commit 680baeffeb (PR #2804)

This caused a stack overflow when comparing a nan with a payload of 1000
or more.

This bug was found by OSS-fuzz.
Ref: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=64771
Fixes GHSA-7hmr-442f-qc8j

It also fixes 1e999999999 > 1e-1147483646   triggering UBSAN errors
Fixes #2968

NEWS.md

@@ -3,7 +3,7 @@
 ## Security
 
 - CVE-2023-50246: ....
-- CVE-2023-50268: ....
+- CVE-2023-50268: fix stack-buffer-overflow if comparing nan with payload
 
 ## CLI changes