Core/SpellScript: allow optional parameters to be passed to FinishCast

followup of 50a3ce5703bdaa4fe16e2e773eabafa9a4818083

src/server/game/Spells/SpellScript.cpp

@@ -624,9 +624,9 @@ SpellInfo const* SpellScript::GetTriggeringSpell()
     return m_spell->m_triggeredByAuraSpell;
 }
 
-void SpellScript::FinishCast(SpellCastResult result)
+void SpellScript::FinishCast(SpellCastResult result, uint32* param1 /*= nullptr*/, uint32* param2 /*= nullptr*/)
 {
-    m_spell->SendCastResult(result);
+    m_spell->SendCastResult(result, param1, param2);
     m_spell->finish(result == SPELL_CAST_OK);
 }