Email: Target number is wrong when many email addresses are missing

[Bagera]

Description

The target number shows as -5 when it should probably be 2 (7 total targets - 5 missing emails)

In this email, there seem to be no targets left, even though the smart search hits 7.

Steps to reproduce

1. Go to (https://app.dev.zetkin.org/organize/1/projects/8/emails/3)
2. Look at the numbers

Screenshots

Activity list

Email page

[kaulfield23]

I'm taking this one!