fix #H8712 - curses menu selector overflow

The curses interface would assign menu selector characters a-z, A-Z,
and then 0-9, but trying to type 0-9 would start a count rather than
select an entry, and if the display was tall enough for more than 62
entries, the ones after '9' were ASCII punctuation characters.
Limit the number of entries per page to 52 + number_of_'$'_entries
(which should be 0 or 1) so that it won't run out of normal letters.

The perm_invent window, if enabled, ought to allow more than that
because it isn't used to make selections and might have an arbtirary
number of '#' overflow entries.  But I'll leave that for somebody
else to tackle.

Tested by temporarily setting the limit to 26 instead of 52 since
I'm not able to display anything tall enough to exercise the latter.

doc/fixes36.3

@@ -1,4 +1,4 @@
-$NHDT-Branch: NetHack-3.6 $:$NHDT-Revision: 1.0 $ $NHDT-Date: 1557526914 2019/05/10 22:21:54 $
+$NHDT-Branch: NetHack-3.6 $:$NHDT-Revision: 1.1 $ $NHDT-Date: 1557569075 2019/05/11 10:04:35 $
 
 This fixes36.3 file is here to capture information about updates in the 3.6.x
 lineage following the release of 3.6.2 in May 2019. Please note, however,
@@ -19,6 +19,9 @@ Fixes to Post-3.6.2 Problems that Were Exposed Via git Repository
 
 Platform- and/or Interface-Specific Fixes or Features
 -----------------------------------------------------
+curses: very tall menus tried to use selector characters a-z, A-Z, and 0-9,
+	but 0-9 should be reserved for counts and if the display was tall
+	enough for more than 62 entries, arbitrary ASCII punctuation got used
 
 
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