Make the unpack task do nothing if externalsrc is in use. This avoids
the following error after having done `devtool modify lsof`:
ERROR: lsof-4.91-r0 do_unpack: Unpack failure for URL:
'file://.../builds/qemux86-64/tmp/work/core2-64-poky-linux/lsof/4.91-r0/lsof_4.91/lsof_4.91_src.tar'.
Unpack command PATH="..." tar x --no-same-owner -f
.../builds/qemux86-64/tmp/work/core2-64-poky-linux/lsof/4.91-r0/lsof_4.91/lsof_4.91_src.tar
failed with return value 2
Signed-off-by: Peter Kjellerstedt <peter.kjellerstedt@axis.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
