Fix explosions hitting their endpoint twice. [2481715]

As of now, explosion beams do not do affect anything until they actually explode. I can't think of any explosions that should do this, but I'm pretty sure there are some that I'm forgetting. Fix a security issue with crash dump reporting.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@8646 c06c8d41-db1a-0410-9941-cceddc491573

Created by  haranp  on January 21, 2009
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