Make draining beams properly take full negative energy resistance into

account.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@8583 c06c8d41-db1a-0410-9941-cceddc491573

Created by  dolorous  on January 19, 2009
HVBIFFGMVMU3J6SCKE5277427L6EMV4WZXI7XXJBE4RBQVBSZILAC
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