xsf: Fix a rather blatant use-after-free (found by Coverity).
aac: Remove unused source file.
aac: Remove useless null check (found by Coverity).
flacng: Fix memory leak (found by Coverity).
sid: Fix memory leak (found by Coverity).
skins: Add missing break (found by Coverity).
ladspa: Fix mutex lock without unlock (found by Coverity).
filewriter: Remove always-false conditional (found by Coverity).
sid: Boolean values are never negative (found by Coverity).