reapply Cmd value even if CmdAdd returns early

Fixes #3762

If an image is built while using the cache and the file of an ADD directive is changed, the CmdAdd function returned early. This will result in an overwriten CMD value of the container, since the value is not reset to it's original value.

This was already handled correctly in the CmdRun and commit function with the same defer function.

Docker-DCO-1.1-Signed-off-by: Maximilian Goisser <goisser94@gmail.com> (github:
hobofan)