Fix an error when navigating away from an unsaved page

diff --git a/WowLua.lua b/WowLua.lua
index 510e313..2b57adb 100644
--- a/WowLua.lua
+++ b/WowLua.lua
@@ -555,7 +555,10 @@ function WowLua:GoToPage(page)
 	end

 	local entry = self:SelectPage(page)
-
+	if not entry then
+        return
+    end
+
 	WowLuaFrameEditBox:SetText(entry.content)
 	self:UpdateButtons()
 	self:SetTitle(false)