Multiple audio objects behave incorrectly with NULL input

[h4yn0nnym0u5e]

For examples see fixes for AudioRecordQueue (PR#403), AudioEffectEnvelope (PR#444), AudioEffectFade (PR#464). Typically this is where the object contains time-dependent state internally, which is not updated as it should be when there is no received audio block (e.g. receiveReadOnly() returns NULL). Silence does not necessarily mean inactivity.