patch 9.1.1926: xdiff: Coverity warning with MAX_CNT/UINT_MAX usage

patch 9.1.1926: xdiff: Coverity warning with MAX_CNT/UINT_MAX usage

Problem:  xdiff: Coverity warning with MAX_CNT/UINT_MAX usage
          (after v9.1.1921)
Solution: Replace XDL_MIN macro to a manual check.
          (Yee Cheng Chin)

In the recent xdiff upstream sync (#18765), MAX_CNT in xhistogram was
switched back to using UINT_MAX to match upstream. This exposed an issue
in xdiff that using using min() to compare against the max integer will
not work as the number will just overflow. Switch the check to be done
in a saturating add that respects integer overflow.

related: #18765
closes: #18792

Signed-off-by: Yee Cheng Chin <ychin.git@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>