[gnome-contacts/nielsdg/link-duplicate-contacts] store: Make sure we don't add individuals twice

[Niels De Graef <nielsdg src gnome org>]

commit 6ba0c4b3fb4684670ef631c67482f1bbd4f7ea86
Author: Niels De Graef <nielsdegraef gmail com>
Date:   Tue Oct 11 10:31:06 2022 +0200

    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

 src/contacts-store.vala | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/src/contacts-store.vala b/src/contacts-store.vala
index 7a70cad6..c359a379 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);
       }
     }