Core/Creature: IsMovementPreventedByCasting followup

Handle correctly move allowed channels: IsChannelActive checks if channel phase has started (after cast if any)
Must skip the other checks since all channels focus target.

ref #19532

src/server/game/Entities/Creature/Creature.cpp

@@ -3108,8 +3108,7 @@ bool Creature::IsMovementPreventedByCasting() const
     {
         if (spell->getState() != SPELL_STATE_FINISHED && spell->IsChannelActive())
             if (spell->GetSpellInfo()->IsMoveAllowedChannel())
-                if (HasUnitState(UNIT_STATE_CASTING))
-                    return true;
+                return false;
     }
 
     if (const_cast<Creature*>(this)->IsFocusing(nullptr, true))