Searching for installed extensions can return results from other (sub)wikis

Follow this steps to reproduce:

• install an extension X on a subwiki A
• go to a different subwiki B where extension X is not installed and open the administration. Go to the Extension Manager section and select the Installed Extensions. Search for extension X.

Current behaviour: you get a result
Expected behaviour: you shouldn't get any results because extension X is not installed on subwiki B.