Instead of allocating space for ((n + 1) * size) (to make room for all
entries plus terminator), it allocated space for (n * size + 1).
init_extended_commands_popup would therefore write past the end of the
memory allocated for command_list and command_indx when trying to store
their respective terminator entries. This meant the X11 windowport
would crash when accessing the extended command menu, if NetHack had
been compiled with -fsanitize=address.
I also did some minor cleanup/refactoring to eliminate variables and
lines that were made redundant or useless by 9d64d13, which changed the
way the function worked and removed the need for things like tracking
indices in the source and destination arrays with separate variables.
44dcf95e04