make location textbox read only

MainWindow.xaml

@@ -112,7 +112,7 @@
                                 <ColumnDefinition Width="Auto"/>
                             </Grid.ColumnDefinitions>
                             <Label Content="Location on disk for the player journal. There is usually no need to change this setting." Grid.Row="0" Grid.ColumnSpan="2" HorizontalAlignment="Left" Margin="0,0,0,0" VerticalAlignment="Top" RenderTransformOrigin="-0.08,0.496"/>
-                            <TextBox x:Name="journallocation" Text="" Grid.Row="1" Grid.Column="0" Margin="5,0,5,10" TextWrapping="Wrap" />
+                            <TextBox x:Name="journallocation" IsReadOnly="true" Text="" Grid.Row="1" Grid.Column="0" Margin="5,0,5,10" TextWrapping="Wrap" />
                             <Button x:Name="browsejournallocation" Content="Browse" Grid.Row="1" Grid.Column="1" Margin="0,0,0,0" Width="Auto" VerticalAlignment="Top" HorizontalAlignment="Left" Click="browsejournallocation_Click"/>
                         </Grid>
                     </GroupBox>

Util/Config.cs

@@ -45,11 +45,15 @@ namespace EliteBGS.Util {
 
         public void SaveGlobal() {
             var serializer = JsonSerializer.CreateDefault();
-            using (var file = new StreamWriter(File.OpenWrite(config_file), Encoding.UTF8)) {
+            using (FileStream filestream = File.OpenWrite(config_file)) {
+                filestream.SetLength(0);
+                filestream.Flush();
+                using (StreamWriter file = new StreamWriter(filestream, Encoding.UTF8)) {
                     var stream = new JsonTextWriter(file);
                     serializer.Serialize(stream, global_config);
                 }
             }
+        }
 
         public void LoadGlobal() {
             var serializer = JsonSerializer.CreateDefault();