System.dll 64bit fixes


git-svn-id: https://svn.code.sf.net/p/nsis/code/NSIS/trunk@6509 212acab6-be3b-0410-9dea-997c60f758d6
Minor typo and indentation fixes


git-svn-id: https://svn.code.sf.net/p/nsis/code/NSIS/trunk@6510 212acab6-be3b-0410-9dea-997c60f758d6