MSVC VST3 Hosting Warning Fixes

Audio Plugins
1

Not sure why the warning C4244 hasn't come up before in this function, but here be some warning fixes:

    tresult PLUGIN_API performEdit (Vst::ParamID paramID, Vst::ParamValue valueNormalized) override
    {
        const int index = getIndexOfParamID (paramID);
        if (index < 0)
            return kResultFalse;
        owner->sendParamChangeMessageToListeners (index, (float) valueNormalized);
        return owner->editController->setParamNormalized (paramID, (float) valueNormalized);
    }