Fixed an error when mousing over an empty spellbook slot

diff --git a/CliqueOptions.lua b/CliqueOptions.lua
index f808d93..b89534c 100644
--- a/CliqueOptions.lua
+++ b/CliqueOptions.lua
@@ -28,7 +28,10 @@ function Clique:OptionsOnLoad()
         button:RegisterForClicks("LeftButtonUp","RightButtonUp", "MiddleButtonUp", "Button4Up", "Button5Up")
         button:SetAllPoints(parent)
         button:SetScript("OnClick", onclick)
-        button:SetScript("OnEnter", SpellButton_OnEnter)
+        button:SetScript("OnEnter", function(self)
+			local parent = self:GetParent()
+			SpellButton_OnEnter(parent)
+		end)
         button:SetScript("OnLeave", onleave)
 		button:Hide()
         self.spellbuttons[i] = button