Reapply "fix for libtotem.lua crashing with Invalid spell slot"

This reverts commit 02d3cd8348.

libs/libspell.lua

@@ -108,6 +108,9 @@ function libspell.GetSpellInfo(index, bookType)
       name = GetSpellName(id, bookType)
     end
   else
+    if not bookType or (bookType ~= BOOKTYPE_SPELL and bookType ~= BOOKTYPE_PET) then
+      return nil
+    end
     name, rank = GetSpellName(index, bookType)
     id, bookType = libspell.GetSpellIndex(name, rank)
   end

libs/libtotem.lua

@@ -252,6 +252,8 @@ end)
 
 -- Hook CastSpell to store pending name/icon per slot
 hooksecurefunc("CastSpell", function(id, bookType)
+  if not id or not bookType then return end
+  if bookType ~= BOOKTYPE_SPELL and bookType ~= BOOKTYPE_PET then return end
   local name, rank, icon, _, _, _, spellId = libspell.GetSpellInfo(id, bookType)
   if not name then return end
   libtotem:CheckAddQueue(name, rank, icon, spellId)