couple of curses symbol handling bits

couple of curses symbol handling bits

Primary and rogue symbols were being set to default if primary hadn't
been given a value, possibly clobbering rogue symbols if those had
been given a value.  Initialize them independenly.

Return early from curses_convert_glyph() if the value doesn't have
the 8th bit set since it now deals exclusively with DECgraphics
handling.  Force a sane value for returning early on rogue level.