fix a segfault in mapglyph reported by Pasi earlier today

fix a segfault in mapglyph reported by Pasi earlier today
 Changes to be committed:
	modified:   src/pager.c

Steps to reproduce the reported segfault:
Use / command, answer n, press space and enter

In do_look() variable glyph is only set to a proper
value if using the screen (from_screen) or the
mouse (clicklook).

On the code path that triggered the segfault,
glyph was being passed to mapglyph with a random
arbitrary value.

If glyph had been initialized at the start of
do_look(), it would have prevented the segfault,
but would have always displayed a giant ant or
something silly instead of the correct thing.

Don't use glyph except under
from_screen || clicklook.