fix bug #21671

wesnoth.synchronize_choice checks the return value of toconfig fcn,
and if it indicated that it partially failed to convert the table,
it will chat a warning, IF wesnoth is running in debug mode
(that is game_config::debug = true, which is determined by e.g.
the command line flag --debug)

changelog

@@ -9,6 +9,10 @@ Version 1.11.11+dev:
      * Fixed missing objective in 'The Court of Karrag'.
  * Language and i18n:
    * Updated translations: German, Slovak
+ * Lua API:
+   * Fix bug #21761: wesnoth.synchronize_choice will now give a warning when 
+     the table returned by the user-specified function is not completely valid,
+     when wesnoth is running in debug mode (--debug command line flag).
  * Units:
    * Increased the experience requirement for the Rami from 32 to 39
    * Increased the experience requirement for the Saree from 56 to 64

src/scripting/lua.cpp

@@ -2652,8 +2652,11 @@ namespace {
 					index = 2;
 			}
 			lua_settop(L, index);
-			if (luaW_pcall(L, 0, 1, false))
-				luaW_toconfig(L, -1, cfg);
+			if (luaW_pcall(L, 0, 1, false)) {
+				if(!luaW_toconfig(L, -1, cfg) && game_config::debug) {
+					chat_message("Lua warning", "function returned to wesnoth.synchronize_choice a table which was partially invalid");
+				}
+			}
 			return cfg;
 		}