image_types_wic: Fix file-checksums for missing files in search path

image_types_wic: Fix file-checksums for missing files in search path

When we tell bitbake about file-checksums, we need to tell it both the files
we look at that exist, but also the ones we looked for but aren't present.

This means that if files appear earlier in the search path, bitbake can then
do the correct things like updating the taskhash and re-running the recipe/task.

In this case, wic was only signalling file presence. This patch adds in the
files it looked at but didn't find too.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>