fix assertion failure when dismissing units

http://gna.org/bugs/?23510

src/dialogs.cpp

@@ -150,8 +150,6 @@ gui::dialog_button_action::RESULT delete_recall_unit::button_pressed(int menu_se
 
 		// Remove the item from filter_textbox memory
 		filter_.delete_item(menu_selection);
-		//add dismissal to the undo stack
-		resources::undo_stack->add_dismissal(u_ptr);
 
 		LOG_DP << "Dismissing a unit, side = " << u.side() << " id = '" << u.id() << "'\n";
 		LOG_DP << "That side's recall list:\n";

src/synced_commands.cpp

@@ -232,6 +232,13 @@ SYNCED_COMMAND_HANDLER_FUNCTION(disband, child, /*use_undo*/, /*show*/, error_ha
 
 	const std::string& unit_id = child["value"];
 	size_t old_size = current_team.recall_list().size();
+
+	// Find the unit in the recall list.
+	unit_ptr dismissed_unit = current_team.recall_list().find_if_matches_id(unit_id);
+	assert(dismissed_unit);
+	//add dismissal to the undo stack
+	resources::undo_stack->add_dismissal(dismissed_unit);
+
 	current_team.recall_list().erase_if_matches_id(unit_id);
 
 	if (old_size == current_team.recall_list().size()) {