AltClickInvite: fix very old lua error

was happening on every moving chat to new window
was preventing newly moved chat to be opened
and producing origin blizz error without reference to LeatrixPlus, that's why it took so long to find

Leatrix_Plus.lua

@@ -9045,17 +9045,16 @@
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         if LeaPlusLC["AltClickInv"] == "On" then
-            local originSetItemRef = SetItemRef;
-            local function HandleAltClick(link, text, button)
-                local linkType, playerName = strsplit(":", link);
-                if linkType == "player" and IsAltKeyDown()
-                then
-                    return InviteUnit(playerName)
-                else
-                    return originSetItemRef(link, text, button)
+            local originSetItemRef = SetItemRef
+            SetItemRef = function(link, text, button, chatFrame)
+                local linkType, playerName = strsplit(":", link)
+                if linkType == "player" and IsAltKeyDown() then
+                    InviteUnit(playerName)
+                    return  -- Prevent Blizzard from opening whisper
                 end
+                -- Otherwise do original Blizzard behavior
+                originSetItemRef(link, text, button, chatFrame)
             end
-            SetItemRef = HandleAltClick;
         end
 
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