qemu-img: Check create_opts before image creation

qemu-img: 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 for the target image in qemu-img convert, which is
important so that the create_opts pointer in img_convert() 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 f75613cf2488a37fb8019bc32a06ddbcd477d0ce)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>