Set DialogResult in AutofireConfig

see #2599

src/BizHawk.Client.EmuHawk/config/AutofireConfig.cs

@@ -60,11 +60,13 @@ namespace BizHawk.Client.EmuHawk
 			_config.AutofireLagFrames = cbConsiderLag.Checked;
 			_stickyXorAdapter.SetOnOffPatternFromConfig(_config.AutofireOn, _config.AutofireOff);
 
+			DialogResult = DialogResult.OK;
 			Close();
 		}
 
 		private void btnDialogCancel_Click(object sender, EventArgs e)
 		{
+			DialogResult = DialogResult.Cancel;
 			Close();
 		}
 	}