misc: avoid crash if no certificate added for device

Using foundAccountDevice with a dht::PkId, can add known devices
without certificates. Iterating over knownDevices_ without checking
any certificate will lead to a segfault.
This will not happen under normal circumstances, because foundAccountDevice
only uses certificates, except for testing purpose

Change-Id: I9bf6682d7d6539c0f905e80995333db0d948c5af

src/jamidht/archive_account_manager.cpp

@@ -527,6 +527,10 @@ ArchiveAccountManager::syncDevices()
         // don't send sync data to ourself
         if (dev.first.toString() == info_->deviceId)
             continue;
+        if (!dev.second.certificate) {
+            JAMI_WARNING("Cannot find certificate for {}", dev.first);
+            continue;
+        }
         auto pk = dev.second.certificate->getSharedPublicKey();
         JAMI_DBG("sending device sync to %s %s",
                  dev.second.name.c_str(),

src/jamidht/contact_list.cpp

@@ -595,6 +595,10 @@ ContactList::getSyncData() const
     }
 
     for (const auto& dev : knownDevices_) {
+        if (!dev.second.certificate) {
+            JAMI_WARNING("No certificate found for {}", dev.first);
+            continue;
+        }
         sync_data.devices.emplace(dev.second.certificate->getLongId(),
                                   KnownDeviceSync {dev.second.name,
                                                    dev.second.certificate->getId()});