Fix Channel Mask validation

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Data/Nodes/Artistic/Mask/ChannelMaskNode.cs

         void ValidateChannelCount()
         {
             int channelCount = SlotValueHelper.GetChannelCount(FindSlot<MaterialSlot>(InputSlotId).concreteValueType);
-            if (channelMask > 1 << channelCount - 1)
+            if (channelMask >= 1 << channelCount)
                 channelMask = -1;
         }