Two filter functions were called wrongly, which made us read from uninitialized values.
Added short comment.
No style changes. The tests will be revisited and extended during an upcoming refactor.
signal_processing_unittests now pass Valgrind.
TEST=signal_processing_unittests
Review URL: https://webrtc-codereview.appspot.com/344015
git-svn-id: http://webrtc.googlecode.com/svn/trunk@1466 4adac7df-926f-26a2-2b94-8c16560cd09d