fix: guard legacy InterfaceOptions globals for CoA client

The CoA client's reworked Settings panel does not expose
InterfaceOptionsCombatPanelNameplateClassColors or
InterfaceOptionsCombatPanelEnemyCastBarsOnNameplates, causing a nil-index
error whenever the Combat options panel was shown. Guard each access in
ClassColours and Castbar.

Kui_Nameplates/Modules/Castbar.lua

@@ -402,13 +402,20 @@ function mod:OnInitialize()
 	self.configChangedFuncs.display.cbheight.ro(sizes.cbheight)
 
 	-- handle default interface cvars & checkboxes
+	-- The CoA client's reworked Settings panel may not expose these legacy
+	-- globals; guard each access so a missing widget cannot error every time
+	-- the Combat options panel is shown.
+	if InterfaceOptionsCombatPanel then
 		InterfaceOptionsCombatPanel:HookScript(
 			"OnShow",
 			function()
+				if InterfaceOptionsCombatPanelEnemyCastBarsOnNameplates then
 					InterfaceOptionsCombatPanelEnemyCastBarsOnNameplates:SetChecked(true)
 					InterfaceOptionsCombatPanelEnemyCastBarsOnNameplates:Disable()
 				end
+			end
 		)
+	end
 	InterfaceOptionsFrame:HookScript(
 		"OnHide",
 		function()

Kui_Nameplates/Modules/ClassColours.lua

@@ -94,11 +94,18 @@ function mod:OnInitialize()
 	self:SetEnabledState(self.db.profile.friendly)
 
 	-- handle default interface cvars & checkboxes
+	-- The CoA client's reworked Settings panel does not expose the legacy
+	-- InterfaceOptionsCombatPanel / NameplateClassColors checkbox, so guard
+	-- every access to avoid indexing a nil global.
+	if InterfaceOptionsCombatPanel then
 		InterfaceOptionsCombatPanel:HookScript("OnShow", function()
+			if InterfaceOptionsCombatPanelNameplateClassColors then
 				InterfaceOptionsCombatPanelNameplateClassColors:Disable()
 				InterfaceOptionsCombatPanelNameplateClassColors:SetChecked(mod.db.profile.enemy)
 				InterfaceOptionsCombatPanelNameplateClassColors.Enable = function() return end
+			end
 		end)
+	end
 	InterfaceOptionsFrame:HookScript("OnHide", function() SetCVars() end)
 	SetCVars()
 end