Fix crash on setting focus when goal is to clear

Author: DSPaul

src/Views/TagEditView.xaml.cs

@@ -14,7 +14,7 @@ public TagEditView()
         }
 
         //makes objects lose focus when clicked away
-        private void MainGrid_MouseDown(object sender, MouseButtonEventArgs e) => MainGrid.Focus();
+        private void MainGrid_MouseDown(object sender, MouseButtonEventArgs e) => Keyboard.ClearFocus();
 
         private void TagNameTextBox_Loaded(object sender, System.Windows.RoutedEventArgs e)
         {

src/Windows/CodexBulkEditWindow.xaml.cs

@@ -18,6 +18,6 @@ public CodexBulkEditWindow(CodexBulkEditViewModel vm)
             ((CodexBulkEditViewModel)DataContext).CloseAction = Close;
         }
 
-        private void MainGrid_MouseDown(object sender, MouseButtonEventArgs e) => MainGrid.Focus();
+        private void MainGrid_MouseDown(object sender, MouseButtonEventArgs e) => Keyboard.ClearFocus();
     }
 }

src/Windows/CodexEditWindow.xaml.cs

@@ -22,7 +22,7 @@ public CodexEditWindow(CodexEditViewModel vm)
             AuthorsComboBox.ApplyTemplate();
         }
 
-        private void MainGrid_MouseDown(object sender, MouseButtonEventArgs e) => MainGrid.Focus();
+        private void MainGrid_MouseDown(object sender, MouseButtonEventArgs e) => Keyboard.ClearFocus();
 
         // https://serialseb.com/blog/2007/09/03/wpf-tips-6-preventing-scrollviewer-from/
         private void treeView_PreviewMouseWheel(object sender, MouseWheelEventArgs e)

src/Windows/MainWindow.xaml.cs

@@ -29,7 +29,7 @@ public MainWindow()
         private readonly MainViewModel MainViewModel;
 
         //Deselects when you click away
-        private void Window_MouseDown(object sender, MouseButtonEventArgs e) => MainGrid.Focus();
+        private void Window_MouseDown(object sender, MouseButtonEventArgs e) => Keyboard.ClearFocus();
 
         private void Window_Closing(object sender, CancelEventArgs e)
         {