misc: chore: Fix numerous NullReferenceExceptions, InvalidOperationExceptions

src/Ryujinx/UI/Controls/ApplicationContextMenu.axaml.cs

@@ -111,7 +111,7 @@ namespace Ryujinx.Ava.UI.Controls
                     viewModel.VirtualFileSystem,
                     viewModel.SelectedApplication.IdString,
                     viewModel.SelectedApplication.Name,
-                    viewModel.SelectedApplication.Path).ShowDialog(viewModel.TopLevel as Window);
+                    viewModel.SelectedApplication.Path).ShowDialog((Window)viewModel.TopLevel);
             }
         }
 
@@ -396,9 +396,12 @@ namespace Ryujinx.Ava.UI.Controls
                     viewModel.SelectedApplication.Name);
 
                 var iconFile = await result[0].CreateFileAsync(selectedApp.IdString + ".png");
-                await using var fileStream = await iconFile.OpenWriteAsync();
+                if (iconFile != null)
+                {
+                    await using var fileStream = await iconFile.OpenWriteAsync();
 
-                fileStream.Write(selectedApp.Icon);
+                    fileStream.Write(selectedApp.Icon);
+                }
             }
         }
 

src/Ryujinx/UI/Controls/ApplicationGridView.axaml.cs

@@ -37,7 +37,7 @@ namespace Ryujinx.Ava.UI.Controls
 
         private void SearchBox_OnKeyUp(object sender, KeyEventArgs args)
         {
-            (DataContext as MainWindowViewModel).SearchText = (sender as TextBox).Text;
+            (DataContext as MainWindowViewModel).SearchText = (sender as TextBox)?.Text;
         }
     }
 }

src/Ryujinx/UI/Controls/ApplicationListView.axaml.cs

@@ -38,7 +38,7 @@ namespace Ryujinx.Ava.UI.Controls
 
         private void SearchBox_OnKeyUp(object sender, KeyEventArgs args)
         {
-            (DataContext as MainWindowViewModel).SearchText = (sender as TextBox).Text;
+            (DataContext as MainWindowViewModel).SearchText = (sender as TextBox)?.Text;
         }
 
         private async void IdString_OnClick(object sender, RoutedEventArgs e)