Wiki statistics displays N/A value in user count column for wikis with no users

[petrenkonikita112263]

Prerequisites

• local XWiki instance 14.10+ with Tomcat servlet and any supported DB
• installed Admin Tools (Pro) 1.0-rc3 on main Wiki

Step to reproduce

1. Create a new wiki with default settings and flavor installed
2. Go to Admin Tools home in main Wiki
3. Click on View usage info for all wikis
4. Observe the result LD table

Actual result

The wiki that was created with no user will have user count 0 with value N/A*

Expected result

The user count column displays only 0 value.