store: Make sure we don't add individuals twice

An individual can appear several times in the `changes` argument of the
`IndividualAggregator`'s `individuals-changed-detailed` signal, in the
case of linking. When 2 Individuals are linked -let's call them A and
B- into a single Individual C, then the signal will be emitted with the
following map:

```
A -> C
B -> C
```

In other words, C will show up twice in the list of values. Since we
weren't checking whether an individual already existed before adding it
to the `to_add` list, duplicates were a possibility. This should no
longer be the case (and from a quick check, it doesn't have any
non-negligible performance impact either).

Fixes: https://gitlab.gnome.org/GNOME/gnome-contacts/-/issues/247
(cherry picked from commit 6ba0c4b3fb4684670ef631c67482f1bbd4f7ea86)

1 files changed, 1 insertions, 1 deletions

diff --git a/src/contacts-store.vala b/src/contacts-store.vala
index 7a70cad..c359a37 100644
--- a/src/contacts-store.vala
+++ b/src/contacts-store.vala
@@ -188,7 +188,7 @@ public class Contacts.Store : GLib.Object {
       if (individual != null)
         to_remove.add (individual);
       foreach (var new_i in changes[individual]) {
-        if (new_i != null)
+        if (new_i != null && !to_add.find (new_i, null))
           to_add.add (new_i);
       }
     }