Crash when Link control is page scoped

If you add a link control to the customItems array and set its scope to page the default value does not appear. Also, clicking on the Set Link button causes Stacks to crash RapidWeaver.

This is the PLIST entry for the Link control:

		<dict>
			<key>default</key>
			<string>https://yoururl.com/image.jpg</string>
			<key>group</key>
			<string>General</string>
			<key>id</key>
			<string>remote-image</string>
			<key>title</key>
			<string>Remote Image</string>
			<key>type</key>
			<string>link</string>
			<key>scope</key>
			<string>page</string>
		</dict>

If you remove the scope key from the Link control everything works as expected -- the default value is displayed and clicking the Set Link button does not crash RapidWeaver.