Don't show filtered from NaN on Groups when 0 groups found

[larssandergreen]

Overview

I know this will be replaced with SK, but it's a simple fix to remove a NaN when using Manage Groups and filtering so 0 groups are found. We don't show the "filtered from" text normally, I think it only shows up when you have zero groups.

Before

After

[civibot]

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[eileenmcnaughton]

makes sense!