Remove useless assignments to NULL in MythDownloadManager. Cppcheck
Fix several issues reported by cppcheck in AudioOutputPulse.

Some of this code is just awful and in dire need of refactoring!
Brace position fixes in mpeg2fix.cpp
Silence an unused variable warning in BufferedSocketDevice::Flush()
mmap returns MAP_FAILED in the event of a failure, so test for that, not a value less than zero.

Reported by cppcheck
Check reply is not null before dereferencing. Cppcheck