re-fix screendump (Stefano Stabellini)

re-fix screendump (Stefano Stabellini)

Removing the assumption about a single graphic console made
get_graphic_console return NULL when called by vga_screen_dump.
In this case returning NULL is correct but since NULL is not handled in
qemu_console_resize it causes a segmentation fault.
Just returning immediately from qemu_console_resize is sufficient to fix the
problem.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6390 c046a42c-6fe2-441c-8c8c-71466251a162