Make name(), base_name() and full_name() return a more informative string (and

be less likely to crash) if given an invalid monster.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@8734 c06c8d41-db1a-0410-9941-cceddc491573

Created by  zelgadis  on January 24, 2009
YWSN3SJEZRDX223KTSDBR7IU5Y7Y7SSKQWTOULWRHQV47UK5M5RQC
Change contents