Don't round bottom corners of asset picker

Corner radius doesn't match that used on 2019 iPad Pro, so rounding the
bottom corners results in the view controller beneath the asset picker
showing through in some split-screen configurations

Tusker/Screens/Asset Picker/AssetPickerSheetContainerViewController.swift

@@ -33,6 +33,8 @@ class AssetPickerSheetContainerViewController: SheetContainerViewController {
     
     override func viewDidLoad() {
         assetPicker.view.layer.cornerRadius = view.bounds.width * 0.02
+        // don't round bottom corners, since they'll always be cut off by the device
+        assetPicker.view.layer.maskedCorners = [.layerMinXMinYCorner, .layerMaxXMinYCorner]
         
         super.viewDidLoad()
     }