patch 9.1.0921: popupmenu logic is a bit convoluted

patch 9.1.0921: popupmenu logic is a bit convoluted

Problem:  popupmenu logic is a bit convoluted
Solution: slightly refactor logic and use MIN/MAX() macros to simplify
          (glepnir)

Define the MAX/MIN macros. Since we support some older platforms, C
compilers may not be as smart. This helps reduce unnecessary if
statements and redundant ternary expressions. Pre-calculate some
expressions by defining variables. Remove unnecessary parentheses.
Adjust certain lines to avoid exceeding 80 columns.

closes: #16205

Signed-off-by: glepnir <glephunter@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>