libcast: make post-hook update last cast texture

we now set lastcasttex from the texture returned by libspell.GetSpellInfo in "CastSpellByName" post-hook

libs/libcast.lua

@@ -400,13 +400,17 @@ hooksecurefunc("CastSpell", function(id, bookType)
   end
 end, true)
 
-hooksecurefunc("CastSpellByName", function(spell, target)
-  _, lastrank = libspell.GetSpellInfo(spell)
+hooksecurefunc("CastSpellByName", function(spellCasted, target)
+  local spellName, rank, texture, _, _, _, cachedId = libspell.GetSpellInfo(spellCasted)
+  if not spellName or not cachedId then return end -- ignore if the spell is not found
+
+  lastrank = rank
+  lastcasttex = texture
 
   for i=1,120 do
     -- detect if any cast is ongoing
     if IsCurrentAction(i) then
-      CastCustom(spell)
+      CastCustom(spellCasted)
       return
     end
   end