Fix wrapping of toplevel gadget callins returning several parameters. (…

…#3947)

Fix wrapping of top level callins returning several parameters, this fixes a bug introduced in #3907
Affected methods: GameSetup, AllowWeaponTarget, UnitPreDamaged, FeaturePreDamaged

Likely affected gadgets:
* GameSetup: none, still it can be affecting some engine calls since it will always return newReady nil, although afaics the engine won't accept the nil value so it shouldn't be affecting it.
* AllowWeaponTarget (affects returned priority): unit_aa_targeting_priority.
* UnitPreDamaged (affects impulse only): unit_combomb_full_damage, unit_dgun_behaviour, engine_hotfixes, unit_paralyze_damage_multiplier, map_lava, unit_paralyze_on_off, unit_collision_damage_behavior, unit_timeslow, unit_objectify, unit_evolution, unit_commando_watch, unit_shield_behaviour, unit_single_damage_fire, unit_lightning_splash_dmg, mo_preventcombomb, scav_spawner_defense, unit_no_land_damage.
* FeaturePreDamaged (affects impulse only): gfx_tree_feller.

luarules/gadgets.lua

@@ -99,7 +99,6 @@ gadgetHandler = {
 }
 
 
-
 -- these call-ins are set to 'nil' if not used
 -- they are setup in UpdateCallIns()
 local callInLists = {
@@ -812,17 +811,18 @@ function gadgetHandler:UpdateCallIn(name)
 		local selffunc = self[name]
 
 		if selffunc ~= nil then
+			-- max 2 return parameters for top level callins!
 			_G[name] = function(...)
 				callinDepth = callinDepth + 1
 
-				local res = selffunc(self, ...)
+				local res1, res2 = selffunc(self, ...)
 
 				callinDepth = callinDepth - 1
 				if reorderNeeded and callinDepth == 0 then
 					self:PerformReorders()
 				end
 
-				return res
+				return res1, res2
 			end
 		else
 			Spring.Log(LOG_SECTION, LOG.ERROR, "UpdateCallIn: " .. name .. " is not implemented")