block: Check create_opts before image creation

block: Check create_opts before image creation

If a driver supports image creation, it needs to set the .create_opts
field. We can use that to make sure .create_opts for both drivers
involved is not NULL in bdrv_img_create(), which is important so that
the create_opts pointer in that function is not NULL after the
qemu_opts_append() calls and when going into qemu_opts_create().

Cc: qemu-stable@nongnu.org
Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
(cherry picked from commit c6149724080af7b3d5d61eac8942655e6d212783)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>