Fix a typo in my previous commit. thanks dr.tenma for pointing this out.

--HG--
branch : trunk

src/game/Spell.cpp

@@ -1390,7 +1390,7 @@ SpellMissInfo Spell::DoSpellHitOnUnit(Unit *unit, const uint32 effectMask, bool
                 if (IsChanneledSpell(m_spellInfo))
                     m_originalCaster->ModSpellCastTime(aurSpellInfo, duration, this);
 
-                if (duration <= 0)
+                if (duration == 0)
                 {
                     m_spellAura->Remove();
                     return SPELL_MISS_IMMUNE;