Fixed InitialFileName for GTK-based file dialog

samples/ControlCatalog/Pages/DialogsPage.xaml.cs

@@ -42,14 +42,15 @@ namespace ControlCatalog.Pages
                 new SaveFileDialog()
                 {
                     Title = "Save file",
-                    Filters = GetFilters()
+                    Filters = GetFilters(),
+                    InitialFileName = "test.txt"
                 }.ShowAsync(GetWindow());
             };
             this.FindControl<Button>("SelectFolder").Click += delegate
             {
                 new OpenFolderDialog()
                 {
-                    Title = "Select folder"
+                    Title = "Select folder",
                 }.ShowAsync(GetWindow());
             };
             this.FindControl<Button>("DecoratedWindow").Click += delegate

src/Avalonia.X11/NativeDialogs/Gtk.cs

@@ -190,6 +190,9 @@ namespace Avalonia.X11.NativeDialogs
         [DllImport(GtkName)]
         public static extern void gtk_file_chooser_set_filename(IntPtr chooser, Utf8Buffer file);
 
+        [DllImport(GtkName)]
+        public static extern void gtk_file_chooser_set_current_name(IntPtr chooser, Utf8Buffer file);
+        
         [DllImport(GtkName)]
         public static extern IntPtr gtk_file_filter_new();
         

src/Avalonia.X11/NativeDialogs/GtkNativeFileDialogs.cs

@@ -91,7 +91,7 @@ namespace Avalonia.X11.NativeDialogs
                 gtk_dialog_add_button(dlg, open, GtkResponseType.Cancel);
             if (initialFileName != null)
                 using (var fn = new Utf8Buffer(initialFileName))
-                    gtk_file_chooser_set_filename(dlg, fn);
+                    gtk_file_chooser_set_current_name(dlg, fn);
             gtk_window_present(dlg);
             return tcs.Task;
         }