Set initial bg to "Theater" internally as well

MultipleMaids/CM3D2/MultipleMaids/Plugin/MultipleMaids.MaidUpdate.cs

@@ -597,6 +597,7 @@ namespace CM3D2.MultipleMaids.Plugin
                     listStyle.padding.left = listStyle.padding.right = listStyle.padding.top = listStyle.padding.bottom = 4;
                     listStyle.fontSize = GetPix(13);
                     GameMain.Instance.BgMgr.ChangeBg("Theater");
+                    bgIndex = bgCombo.selectedItemIndex = Array.FindIndex(bgArray, bg => bg == "Theater");
                     if (!isVR)
                     {
                         GameMain.Instance.MainCamera.Reset(CameraMain.CameraType.Target, true);