monitor: fix oob command leak

monitor: fix oob command leak

Spotted by ASAN, during make check...

Direct leak of 40 byte(s) in 1 object(s) allocated from:
    #0 0x7f8e27262c48 in malloc (/lib64/libasan.so.5+0xeec48)
    #1 0x7f8e26a5f3c5 in g_malloc (/lib64/libglib-2.0.so.0+0x523c5)
    #2 0x555ab67078a8 in qstring_from_str /home/elmarco/src/qq/qobject/qstring.c:67
    #3 0x555ab67071e4 in qstring_new /home/elmarco/src/qq/qobject/qstring.c:24
    #4 0x555ab6713fbf in qstring_from_escaped_str /home/elmarco/src/qq/qobject/json-parser.c:144
    #5 0x555ab671738c in parse_literal /home/elmarco/src/qq/qobject/json-parser.c:506
    #6 0x555ab67179c3 in parse_value /home/elmarco/src/qq/qobject/json-parser.c:569
    #7 0x555ab6715123 in parse_pair /home/elmarco/src/qq/qobject/json-parser.c:306
    #8 0x555ab6715483 in parse_object /home/elmarco/src/qq/qobject/json-parser.c:357
    #9 0x555ab671798b in parse_value /home/elmarco/src/qq/qobject/json-parser.c:561
    #10 0x555ab6717a6b in json_parser_parse_err /home/elmarco/src/qq/qobject/json-parser.c:592
    #11 0x555ab4fd4dcf in handle_qmp_command /home/elmarco/src/qq/monitor.c:4257
    #12 0x555ab6712c4d in json_message_process_token /home/elmarco/src/qq/qobject/json-streamer.c:105
    #13 0x555ab67e01e2 in json_lexer_feed_char /home/elmarco/src/qq/qobject/json-lexer.c:323
    #14 0x555ab67e0af6 in json_lexer_feed /home/elmarco/src/qq/qobject/json-lexer.c:373
    #15 0x555ab6713010 in json_message_parser_feed /home/elmarco/src/qq/qobject/json-streamer.c:124
    #16 0x555ab4fd58ec in monitor_qmp_read /home/elmarco/src/qq/monitor.c:4337
    #17 0x555ab6559df2 in qemu_chr_be_write_impl /home/elmarco/src/qq/chardev/char.c:175
    #18 0x555ab6559e95 in qemu_chr_be_write /home/elmarco/src/qq/chardev/char.c:187
    #19 0x555ab6560127 in fd_chr_read /home/elmarco/src/qq/chardev/char-fd.c:66
    #20 0x555ab65d9c73 in qio_channel_fd_source_dispatch /home/elmarco/src/qq/io/channel-watch.c:84
    #21 0x7f8e26a598ac in g_main_context_dispatch (/lib64/libglib-2.0.so.0+0x4c8ac)

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20180809114417.28718-4-marcandre.lureau@redhat.com>
[Screwed up in commit b27314567d4]
Cc: qemu-stable@nongnu.org
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>