json: Fix check for unbalanced right curly brace

json: Fix check for unbalanced right curly brace

We immediately diagnose unbalanced right curly brace:

    $ qemu-kvm --nodefaults --nographic --qmp stdio
    {"QMP": {"version": {"qemu": {"micro": 91, "minor": 2, "major": 4},
    "package": "v5.0.0-rc1-1-gf6ce4a439a08"}, "capabilities": ["oob"]}}
    }
    {"error": {"class": "GenericError", "desc": "JSON parse error,
    expecting value"}}

except within square bracket:

    [}

The check for unbalanced braces has a typo.  Fix it.

Fixes: 8d3265b3d00db1071d1d3bf8433b4818088fdeb5
Signed-off-by: Simran Singhal <singhalsimran0@gmail.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20200402182848.GA3023@simran-Inspiron-5558>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
[Commit message rewritten to explain what's broken]
Signed-off-by: Markus Armbruster <armbru@redhat.com>