refactor: commit message editor (#2096)

- When using `SourceGit` as standalone commit message editor, always quits with code `0`.
- Use hotkey `ESC` and dialog titlebar button instead of a custom `OK` button to close this window.

src/Views/CommitMessageEditor.axaml

@@ -37,12 +37,10 @@
 
     <StackPanel Grid.Row="1" Orientation="Vertical" Margin="8">
       <v:CommitMessageToolBox x:Name="Editor" Height="400"/>
-      <Button Classes="flat primary"
-              Width="80"
-              Margin="0,8,0,4"
-              Content="{DynamicResource Text.Sure}"
-              Click="SaveAndClose"
-              HorizontalAlignment="Center"/>
+      <Button Width="0" Height="0"
+              Margin="0" Padding="0"
+              Click="OnCloseByHotKey"
+              HotKey="Escape"/>
     </StackPanel>
   </Grid>
 </v:ChromelessWindow>

src/Views/CommitMessageEditor.axaml.cs

@@ -60,19 +60,18 @@ namespace SourceGit.Views
         {
             base.OnClosed(e);
 
+            _onSave?.Invoke(Editor.CommitMessage);
+
             if (_shouldExitApp)
-                App.Quit(_exitCode);
+                App.Quit(0);
         }
 
-        private void SaveAndClose(object _1, RoutedEventArgs _2)
+        private void OnCloseByHotKey(object sender, RoutedEventArgs e)
         {
-            _onSave?.Invoke(Editor.CommitMessage);
-            _exitCode = 0;
             Close();
         }
 
         private Action<string> _onSave = null;
         private bool _shouldExitApp = true;
-        private int _exitCode = -1;
     }
 }