lib/oe/package_manager: avoid traceback with no packages

If you were using deb packaging, had buildhistory enabled and produced
an SDK that contained no packages in one of the sysroots (such as with
uninative-tarball) then the do_populate_sdk was failing with a python
traceback because there were no fields to split in the output line.

(From OE-Core rev: a0eb3ebbc82133ad239a752a4a85d154be31a311)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oe/package_manager.py

@@ -446,6 +446,8 @@ class DpkgPkgsList(PkgsList):
         if format == "file":
             tmp_output = ""
             for line in tuple(output.split('\n')):
+                if not line.strip():
+                    continue
                 pkg, pkg_file, pkg_arch = line.split()
                 full_path = os.path.join(self.rootfs_dir, pkg_arch, pkg_file)
                 if os.path.exists(full_path):