futility/updater: Check that image exists before digging into it

Found by Coverity Scan

BUG=none
BRANCH=none
TEST=none

Change-Id: I2544a4e84ecadc262e08aaa4e6f056d710d807f5
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/1771972
Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Tested-by: Patrick Georgi <pgeorgi@chromium.org>
Commit-Queue: Patrick Georgi <pgeorgi@chromium.org>
1 file changed