realcmds might point exactly to cmdline, so zeroing cmdline-2 may not affect it
instead, zero cmdline-2, cmdline-1, cmdline and cmdline+1 (entire " /D=")
git-svn-id: https://svn.code.sf.net/p/nsis/code/NSIS/trunk@4967 212acab6-be3b-0410-9dea-997c60f758d6