Fixed a typo in the normal stats metatable add function

diff --git a/WeightsWatcher.lua b/WeightsWatcher.lua
index f254cf5..f508594 100644
--- a/WeightsWatcher.lua
+++ b/WeightsWatcher.lua
@@ -12,7 +12,7 @@ ww_normalStatsMetatable = {
 	__add = function(tbl1, tbl2)
 		local tbl = setmetatable({}, ww_normalStatsMetatable)

-		if tbl ~= nil then
+		if tbl1 ~= nil then
 			for k, v in pairs(tbl1) do
 				tbl[k] = v
 			end