classes/license: copy licenses even if there are no checksummed files
Previously do_populate_lic would bail writing the license files (such as the MIT
license text) to deploy/licenses/${PN}/ if there were no files listed in
LIC_FILES_CHKSUM. In general this isn't a problem since LIC_FILES_CHKSUM was
effectively a required field, and for packages which don't have traditional
content was generally set to a separate license such as
${COREBASE}/meta/COPYING.MIT.
However LIC_FILES_CHKSUM is now only required if there are sources in SRC_URI,
so oe-core
b18fa5f removed these now redundant values. The unexpected side
effect of this is that that recipes that generate their content (such as
os-release) or are otherwise "interesting" (such as perf) don't have their
license files copied over, resulting in warnings from do_rootfs.
Resolve this by not returning early if LIC_FILES_CHKSUM is empty, and always
copy the references license files.
Signed-off-by: Ross Burton <ross.burton@intel.com>
