Beanshell dependency cannot be removed if the dependency file is missing

If a beanshell dependency is missing it can't be unselected from the list of jar files.

To reproduce:
Create a beanshell
Select a jar file from the lib folder in the 'Dependencies' tab
Click Apply
Remove the jar file from the lib folder
Click Apply
Unselect the now missing jar file
Click Apply - the missing jar will be reselected.