avatars: invalidate cache when changing account

Prevents 1 to 1 conversations of the same id on different accounts
(local) from having the same avatar after switching account.

Change-Id: Id30af117b2da8bd35d64b54f2e02cbbed0710848
Gitlab: #466

src/avatarregistry.cpp

@@ -56,6 +56,7 @@ AvatarRegistry::addOrUpdateImage(const QString& id)
 void
 AvatarRegistry::connectAccount()
 {
+    uidMap_.clear();
     connect(lrcInstance_->getCurrentContactModel(),
             &ContactModel::profileUpdated,
             this,