Users shouldn't be able to delete all history for a page

Steps to follow to reproduce:

• create a new page and go to edit mode
• type "test" and save the document a couple of times in order to create multiple versions
• click "save & view"
• go to History and delete all versions

Result: The following message appears: "Error number 4001 in 4: Error while parsing velocity page /templates/historyinline.vm Wrapped Exception: Failed to evaluate content with id [/templates/historyinline.vm]"

Suggestion: Users shouldn't be able to delete the current version