vnc: don't crash getting server info if lsock is NULL

When VNC is started with '-vnc none' there will be no
listener socket present. When we try to populate the
VncServerInfo we'll crash accessing a NULL 'lsock'
field.

 #0  qio_channel_socket_get_local_address (ioc=0x0, errp=errp@entry=0x7ffd5b8aa0f0) at io/channel-socket.c:33
 #1  0x00007f4b9a297d6f in vnc_init_basic_info_from_server_addr (errp=0x7ffd5b8aa0f0, info=0x7f4b9d425460, ioc=<optimized out>)  at ui/vnc.c:146
 #2  vnc_server_info_get (vd=0x7f4b9e858000) at ui/vnc.c:223
 #3  0x00007f4b9a29d318 in vnc_qmp_event (vs=0x7f4b9ef82000, vs=0x7f4b9ef82000, event=QAPI_EVENT_VNC_CONNECTED) at ui/vnc.c:279
 #4  vnc_connect (vd=vd@entry=0x7f4b9e858000, sioc=sioc@entry=0x7f4b9e8b3a20, skipauth=skipauth@entry=true, websocket=websocket @entry=false) at ui/vnc.c:2994
 #5  0x00007f4b9a29e8c8 in vnc_display_add_client (id=<optimized out>, csock=<optimized out>, skipauth=<optimized out>) at ui/v nc.c:3825
 #6  0x00007f4b9a18d8a1 in qmp_marshal_add_client (args=<optimized out>, ret=<optimized out>, errp=0x7ffd5b8aa230) at qmp-marsh al.c:123
 #7  0x00007f4b9a0b53f5 in handle_qmp_command (parser=<optimized out>, tokens=<optimized out>) at /usr/src/debug/qemu-2.6.0/mon itor.c:3922
 #8  0x00007f4b9a348580 in json_message_process_token (lexer=0x7f4b9c78dfe8, input=0x7f4b9c7350e0, type=JSON_RCURLY, x=111, y=5 9) at qobject/json-streamer.c:94
 #9  0x00007f4b9a35cfeb in json_lexer_feed_char (lexer=lexer@entry=0x7f4b9c78dfe8, ch=125 '}', flush=flush@entry=false) at qobj ect/json-lexer.c:310
 #10 0x00007f4b9a35d0ae in json_lexer_feed (lexer=0x7f4b9c78dfe8, buffer=<optimized out>, size=<optimized out>) at qobject/json -lexer.c:360
 #11 0x00007f4b9a348679 in json_message_parser_feed (parser=<optimized out>, buffer=<optimized out>, size=<optimized out>) at q object/json-streamer.c:114
 #12 0x00007f4b9a0b3a1b in monitor_qmp_read (opaque=<optimized out>, buf=<optimized out>, size=<optimized out>) at /usr/src/deb ug/qemu-2.6.0/monitor.c:3938
 #13 0x00007f4b9a186751 in tcp_chr_read (chan=<optimized out>, cond=<optimized out>, opaque=0x7f4b9c7add40) at qemu-char.c:2895
 #14 0x00007f4b92b5c79a in g_main_context_dispatch () from /lib64/libglib-2.0.so.0
 #15 0x00007f4b9a2bb0c0 in glib_pollfds_poll () at main-loop.c:213
 #16 os_host_main_loop_wait (timeout=<optimized out>) at main-loop.c:258
 #17 main_loop_wait (nonblocking=<optimized out>) at main-loop.c:506
 #18 0x00007f4b9a0835cf in main_loop () at vl.c:1934
 #19 main (argc=<optimized out>, argv=<optimized out>, envp=<optimized out>) at vl.c:4667

Do an upfront check for a NULL lsock and report an error to
the caller, which matches behaviour from before

  commit 04d2529da27db512dcbd5e99d0e26d333f16efcc
  Author: Daniel P. Berrange <berrange@redhat.com>
  Date:   Fri Feb 27 16:20:57 2015 +0000

    ui: convert VNC server to use QIOChannelSocket

where getsockname() would be given a FD value -1 and thus report
an error to the caller.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-id: 1470134726-15697-2-git-send-email-berrange@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
