The test if a file can fit in an image considers the current offset
twice. So a image that would fit is too big.
Thanks-to: Michael Kurz <michi.kurz@googlemail.com>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@21445 3c298f89-4303-0410-b956-a3cf2f4a3e73