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)

int AecCreate(preproc_effect_t *effect)
{
    webrtc::EchoControlMobile *aec = effect->session->apm->echo_control_mobile();
    ALOGV("AecCreate got aec %p", aec);
 if (aec == NULL) {
        ALOGW("AgcCreate Error");
 return -ENOMEM;
 }
    effect->engine = static_cast<preproc_fx_handle_t>(aec);
 AecInit (effect);
 return 0;
}

int AecCreate(preproc_effect_t *effect)
{
    webrtc::EchoControlMobile *aec = effect->session->apm->echo_control_mobile();
    ALOGV("AecCreate got aec %p", aec);
 if (aec == NULL) {
        ALOGW("AgcCreate Error");
 return -ENOMEM;
 }
    effect->engine = static_cast<preproc_fx_handle_t>(aec);
 AecInit (effect);
 return 0;
}
