[mod_auth] fix base64_decode (#2484)

git-svn-id: svn://svn.lighttpd.net/lighttpd/branches/lighttpd-1.4.x@2871 152afb58-edef-0310-8abb-c4023f1b3aa9
fix some bugs found with canalyze (fixes #2484, thx Zhenbo Xu)

git-svn-id: svn://svn.lighttpd.net/lighttpd/branches/lighttpd-1.4.x@2872 152afb58-edef-0310-8abb-c4023f1b3aa9
fix undefined stuff found with clang

git-svn-id: svn://svn.lighttpd.net/lighttpd/branches/lighttpd-1.4.x@2873 152afb58-edef-0310-8abb-c4023f1b3aa9