bug#35938: Epiphany crashes after adding Firefox Sync account

[Jonathan Frederickson]

Hey, so I just ran into a crash after logging into my Firefox Sync
account in Epiphany:

Steps to reproduce
==================

* Install Epiphany
* Log into Firefox account in settings
* Enable syncing of all resources (though I think it's bookmarks that
  did it
* Click "Sync Now"

Result
======

Epiphany crashes on sync attempt, and again each time it's started.

System details
==============

Generation 4    May 26 2019 15:38:50    (current)
  guix 45bdb66
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: master
    commit: 45bdb6625115959dbf3874b69f89dd506b68fbb6

Logs
====

address@hidden ~$ epiphany 

(epiphany:23099): GLib-CRITICAL **: 20:17:27.455:
g_sequence_get_begin_iter: assertion 'seq != NULL' failed

(epiphany:23099): GLib-CRITICAL **: 20:17:27.455:
g_sequence_iter_is_end: assertion 'iter != NULL' failed

(epiphany:23099): GLib-CRITICAL **: 20:17:27.455: g_sequence_get:
assertion 'iter != NULL' failed **
ERROR:../epiphany-3.28.3.1/src/bookmarks/ephy-bookmark.c:404:ephy_bookmark_add_tag:
assertion failed: (tag != NULL) Aborted