Description of problem:
When disabling a service using cockpit, cockpitd crashes.

Version-Release number of selected component (if applicable):
cockpit-0.27-2.fc21.x86_64

How reproducible:
Seems to happen every time.

Steps to Reproduce:
1.Log into cockpit.
2.In 'Services' click on an enabled service
3.Click 'Disable'

Additional info:
Journal messages from that action:

Dec 17 16:13:14 cyberelk cockpit-agent[2274]: Reauthorizing unix-user:tim
Dec 17 16:13:14 cyberelk cockpit-agent[2274]: cockpit-polkit: user tim was reauthorized
Dec 17 16:13:14 cyberelk cockpit-agent[2274]: cockpit-polkit helper exited with status: 0
Dec 17 16:13:14 cyberelk polkitd[911]: Operator of unix-session:3 successfully authenticated as unix-user:tim to gain ONE-SHOT authorization for action org.freedesktop.policykit.exec for unix-process:2418:36749 [/usr/libexec/cockpitd] (owned by unix-user:tim)
Dec 17 16:13:14 cyberelk pkexec[2447]: pam_unix(polkit-1:session): session opened for user root by (uid=1000)
Dec 17 16:13:14 cyberelk pkexec[2447]: tim: Executing command [USER=root] [TTY=unknown] [CWD=/] [COMMAND=/usr/bin/systemctl disable rngd.service]
Dec 17 16:13:14 cyberelk com.redhat.Cockpit[2308]: Removed symlink /etc/systemd/system/multi-user.target.wants/rngd.service.
Dec 17 16:13:14 cyberelk systemd[1]: Configuration file /usr/lib/systemd/system/auditd.service is marked world-inaccessible. This has no effect as configuration data is accessible via APIs without restrictions. Proceeding anyway.
Dec 17 16:13:14 cyberelk systemd[1]: Unknown serialization item 'subscribed=:1.0'
Dec 17 16:13:14 cyberelk systemd[1]: Unknown serialization item 'subscribed=:1.52'
Dec 17 16:13:14 cyberelk systemd[1]: Configuration file /usr/lib/systemd/system/wpa_supplicant.service is marked executable. Please remove executable permission bits. Proceeding anyway.
Dec 17 16:13:14 cyberelk systemd[1]: Configuration file /usr/lib/systemd/system/wpa_supplicant.service is marked executable. Please remove executable permission bits. Proceeding anyway.
Dec 17 16:13:14 cyberelk kernel: cockpitd[2418]: segfault at 20 ip 00007f78f101a2f8 sp 00007fff367223f0 error 6 in libglib-2.0.so.0.4200.1[7f78f0ffa000+137000]

Similar retrace problem:
https://retrace.fedoraproject.org/faf/problems/422924/
(but line 146 instead of 145, so 'Description' not 'Id')

Backtrace:
#0  g_bit_lock (address=address@entry=0x20, lock_bit=lock_bit@entry=0)
    at gbitlock.c:209
209	  __asm__ volatile goto ("lock bts %1, (%0)\n"
No locals.
#1  0x00007f78f107ea57 in g_variant_lock (value=value@entry=0x0)
    at gvariant-core.c:221
221	  g_bit_lock (&value->state, 0);
No locals.
#2  g_variant_get_data (value=value@entry=0x0) at gvariant-core.c:860
860	  g_variant_lock (value);
No locals.
#3  0x00007f78f107d81c in g_variant_get (value=value@entry=0x0, 
    format_string=format_string@entry=0x46587c "&s") at gvariant.c:5300
        ap = {{gp_offset = 72, fp_offset = 0, overflow_arg_area = 0x1, 
            reg_save_area = 0x50}}
        __FUNCTION__ = "g_variant_get"
5300	    g_variant_get_data (value);
#4  0x0000000000423b26 in on_unit_proxy_ready (object=<optimized out>, 
    res=<optimized out>, user_data=0x75dbc0) at src/daemon/services.c:145
145	      g_variant_get (n, "&s", &name);
        description = 0x7f78f13318c0 <g_source_callback_funcs> ""
        d = <optimized out>
        a = 0x0
        load_state = 0x0
        active_state = 0x0
        sub_state = 0x7495a0 "\001"
        file_state = 0x7f78f13318c0 <g_source_callback_funcs> ""
        n = <optimized out>
        name = 0x7495a0 "\001"
        l = 0x0
        s = 0x0
        f = 0x0
        services = 0x75dbc0
        unit = 0x971e10