audio effects: fix heap overflow

Check consistency of effect command reply sizes before
copying to reply address.

Also add null pointer check on reply size.
Also remove unused parameter warning.

Bug: 21953516.
Change-Id: I4cf00c12eaed696af28f3b7613f7e36f47a160c4
(cherry picked from commit 0f714a464d2425afe00d6450535e763131b40844)

void Visualizer_getConfig(VisualizerContext *pContext, effect_config_t *pConfig)
{
 *pConfig = pContext->mConfig;
}

void Visualizer_getConfig(VisualizerContext *pContext, effect_config_t *pConfig)
{
 *pConfig = pContext->mConfig;
}
