Wait on ContinueOnItemLoad for inbox, panel and loot history items

The inbox package border now waits for the item to load, since another
player's item may not be cached. The panel and loot history drop their
cached branch: ContinueOnItemLoad runs at once for a cached item. The
swing timer reads the off-hand inventory type from the slot instead of
parsing the item link.

skins/blizzard/mail.lua

@@ -63,14 +63,19 @@ pfUI:RegisterSkin("Mailbox", function ()
       SkinButton(OpenMailPackageButton, nil, nil, nil, OpenMailPackageButtonIconTexture)
 
       hooksecurefunc("InboxFrame_OnClick", function(index)
+        OpenMailPackageButton:SetBackdropBorderColor(GetStringColor(pfUI_config.appearance.border.color))
+
+        -- another player's item may not be cached yet
         local _, itemID = GetInboxItemLink(index)
-        if itemID then
-          local quality = C_Item.GetItemQualityByID(itemID)
-          local r,g,b = GetItemQualityColor(quality)
-          OpenMailPackageButton:SetBackdropBorderColor(r,g,b,1)
-        else
-          OpenMailPackageButton:SetBackdropBorderColor(GetStringColor(pfUI_config.appearance.border.color))
-        end
+        if not itemID then return end
+        local item = Item:CreateFromItemID(itemID)
+        item:ContinueOnItemLoad(function()
+          local quality = item:GetItemQuality()
+          if quality and InboxFrame.openMailID == index then
+            local r,g,b = GetItemQualityColor(quality)
+            OpenMailPackageButton:SetBackdropBorderColor(r,g,b,1)
+          end
+        end)
       end)
     end