Fix beams crashing if beam_source was MHITNOT or MHITYOU.

bolt::agent() could still use more work.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@7242 c06c8d41-db1a-0410-9941-cceddc491573

Created by  haranp  on October 13, 2008
PZAU2T5ARMRW76OMMHGK25QK4HRQV3HOXFNFZ2Z72HNOLET7W35QC
Change contents