[Ohrrpgce] SVN: teeemcee/11282 Fix and shrink Sell menu for inventory sizes less than a screenful, fixi

[subversion at HamsterRepublic.com]

teeemcee
2019-08-21 21:45:53 -0700 (Wed, 21 Aug 2019)
704
Fix and shrink Sell menu for inventory sizes less than a screenful, fixing gh#11 crash

If it was smaller than a screen, then itflashed horribly with OUTOFRANGE!
messages, likely crashing.  Ironically that bug was introduced in nightlies by
r10326, which added (incorrectly one-sided) bounds checking for the `top`
variable.

I didn't realise until finishing that the regular Items menu does not yet shrink
to a smaller size, heh. Code dup is bad.

Also code cleanup, add rowsize, pagepage, rowheight variables/constants, so that
the menu is very close to supporting other inventory configurations (I think
that only the width of each inventory slot would need to be changed).

Also fixed wonky scrollbar
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U   wip/menustuf.rbas