Fix error in AudioEffect command status reporting.

AudioEffect::command() should not interpret the status
returned in pReplyData unless the command is ENABLE or
DISABLE.

Also fixed:
- bug in Visualizer::getWAveForm() status reporting.
- wrong initialization value for capture buffer in visualizer engine.

Change-Id: I60fb0011f9dba96ee74661dec1e8ef441edcaf35