Clipboard dialog indicates that it is empty when it isn't fully empty

xfce4-clipman-plugin 1.6.2

Steps to reproduce this issue:

1. xfce4-panel -r (or: activate the "Clear history" menu item)
2. echo -n "1.2.4" | xclip -i
3. Left-click the clipboard icon in the Xfce panel

Screenshot of the result:

Expected result:

• There should be no "Clipboard is empty" menu item
• The "Clear history" button shouldn't be disabled