Refuse a TM/HM on a species with no tmhm list instead of crashing

ItemEffects.use walked speciesDef.tmhm with a bare ipairs() to check
whether the species could learn the machine's move. A record with no
tmhm field at all -- a mod species that never set one, or any record
missing it for whatever reason -- hit ipairs(nil) and took the whole
game down on the first TM/HM use, rather than reaching the ordinary
"can't learn that move" refusal a species whose list simply omits the
move already gets.

An absent list now reads the same as an empty one: nothing to learn,
same refusal, same sound, same text.

src/inventory/ItemEffects.lua

@@ -515,7 +515,10 @@ function ItemEffects.use(data, save, itemId, target, battle, moveIndex, ow)
     if not target then return "failed", { noEffect(data) } end
     local speciesDef = data.pokemon[target.species]
     local ok = false
-    for _, m in ipairs(speciesDef.tmhm) do
+    -- a species record with no tmhm list at all is "teaches nothing", the
+    -- same as one whose list just does not name this move -- not a reason
+    -- to crash instead of refusing normally
+    for _, m in ipairs(speciesDef.tmhm or {}) do
       if m == itemDef.machine.move then ok = true break end
     end
     if not ok then