qxl-render: add more sanity checks

Damn, the dirty rectangle values are signed integers.  So the checks
added by commit 788fbf042fc6d5aaeab56757e6dad622ac5f0c21 are not good
enough, we also have to make sure they are not negative.

[ Note: There must be something broken in spice-server so we get
  negative values in the first place.  Bug opened:
  https://bugzilla.redhat.com/show_bug.cgi?id=1135372 ]

Cc: qemu-stable@nongnu.org
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
spice: use console index as display id

... instead of maintaining our own numbering.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Merge remote-tracking branch 'remotes/spice/tags/pull-spice-20140902-1' into staging

sanity check for qxl, minor spice display channel tweak.

# gpg: Signature made Tue 02 Sep 2014 09:53:39 BST using RSA key ID D3E87138
# gpg: Good signature from "Gerd Hoffmann (work) <kraxel@redhat.com>"
# gpg:                 aka "Gerd Hoffmann <gerd@kraxel.org>"
# gpg:                 aka "Gerd Hoffmann (private) <kraxel@gmail.com>"

* remotes/spice/tags/pull-spice-20140902-1:
  spice: use console index as display id
  qxl-render: add more sanity checks

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>