sync: Do not fail SyncAddTriggerToSyncObject()

We do not want to return a failure at the very last step in
SyncInitTrigger() after having all changes applied.

SyncAddTriggerToSyncObject() must not fail on memory allocation, if the
allocation of the SyncTriggerList fails, trigger a FatalError() instead.

Related to CVE-2025-26601, ZDI-CAN-25870

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Part-of: <!1828>