QAudioInput forces to use 100% volume on initialization

The fix for this issue has introduced a regression. The volume level for a QAudioInput device is now always forced to 100% on initialization whereas before the change it was left untouched. This is particularly unhelpful as there is no way I can see with Qt to read the volume level before initialization with the intention of using QAudioInput::setVolume() to reset it. Another issue is that many hardware audio devices have front-end gain which is likely to cause distortion as the 100% setting will be at maximum gain.

This change will force us to add an unnecessary input volume slider for which we cannot easily label the ticks in dB without delving into the MS Multimedia APIs to get the min. max, and step dB values for the underlying hardware. E.g. on a RealTek HD Audio sound card the levels range from -17.2 dB to +12 dB but on an audio loopback device the range is -96 dB to 0dB.