Description of problem:
The latest `dnf update` upgraded the json-c library from json-c-0.12.1-2.fc26.x86_64 to 0.12.1-5.fc26.x86_64 (on my system) and the new version yields crashes in libu2f. This breaks user login if the u2f pam module is enabled.


Version-Release number of selected component (if applicable):
json-c-0.12.1-5.fc26.x86_64
pam-u2f-1.0.4-3.fc26.x86_64


How reproducible: always


Steps to Reproduce:
1. u2f-host -a register -o https://memyself.example.org
2. paste: { "challenge": "1", "version": "U2F_V2", "appId": "a"}
3. yield EOT: ENTER, CTRL+D

Actual results:
u2f-host: json_object.c:159: json_object_put: Assertion `jso->_ref_count > 0' failed.
zsh: abort (core dumped)  u2f-host -a register -o https://memyself.example.org

And:

systemd-coredump[4051]: Process 4049 (u2f-host) of user 1000 dumped core.
                                                      
                                                      Stack trace of thread 4049:
                                                      #0  0x00007f247b6ef9fb raise (libc.so.6)
                                                      #1  0x00007f247b6f1800 abort (libc.so.6)
                                                      #2  0x00007f247b6e80da __assert_fail_base (libc.so.6)
                                                      #3  0x00007f247b6e8152 __assert_fail (libc.so.6)
                                                      #4  0x00007f247b2ad26a json_object_put (libjson-c.so.2)
                                                      #5  0x00007f247ba90aad prepare_browserdata (libu2f-host.so.0)
                                                      #6  0x00007f247ba9005f u2fh_register (libu2f-host.so.0)
                                                      #7  0x000055ce9671c44c main (u2f-host)
                                                      #8  0x00007f247b6d988a __libc_start_main (libc.so.6)
                                                      #9  0x000055ce9671c54a _start (u2f-host)


Expected results:
No core dump.

Additional info:
The failure in the pam module is similar, but requires a little bit more effort to setup.

Basically you insert on top of /etc/pam.d/login:

auth requisite pam_u2f.so authfile=/etc/u2f_map interactive debug

See `pamu2fcfg` for details on how the u2f_map should look like.

The core dump then:

systemd-coredump[3721]: Process 3586 (login) of user 0 dumped core.
                                                      
                                                      Stack trace of thread 3586:
                                                      #0  0x00007f6bf47dd9fb raise (libc.so.6)
                                                      #1  0x00007f6bf47df800 abort (libc.so.6)
                                                      #2  0x00007f6bf47d60da __assert_fail_base (libc.so.6)
                                                      #3  0x00007f6bf47d6152 __assert_fail (libc.so.6)
                                                      #4  0x00007f6bf34e826a json_object_put (libjson-c.so.2)
                                                      #5  0x00007f6bf3afeaad prepare_browserdata (libu2f-host.so.0)
                                                      #6  0x00007f6bf3afe40a u2fh_authenticate (libu2f-host.so.0)
                                                      #7  0x00007f6bf3d095d3 do_authentication (pam_u2f.so)
                                                      #8  0x00007f6bf3d0833b pam_sm_authenticate (pam_u2f.so)
                                                      #9  0x00007f6bf51d3e71 _pam_dispatch (libpam.so.0)
                                                      #10 0x00007f6bf51d373b pam_authenticate (libpam.so.0)
                                                      #11 0x00005609eb7b7d7c main (login)
                                                      #12 0x00007f6bf47c788a __libc_start_main (libc.so.6)
                                                      #13 0x00005609eb7b8a8a _start (login)