image.bbclass: Only append to IMAGE_LINK_NAME if it was already set
create_symlinks does not create any links if IMAGE_LINK_NAME is empty.
Unfortunately, setup_debugfs_variables unconditionally appends '-dbg' which
results in a previously-empty IMAGE_LINK_NAME containing just '-dbg'. Let's
check that it's not empty before appending.
Signed-off-by: Mike Crowe <mac@mcrowe.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
