ProfilesCheck: fix handling of profiles with neg_action package

When a "packages" file under a profile declares "-*" (meaning to remove
all defaults), pkgcore pushes a special token (`True`) into the packages
set. This is taken by ProfileStack to clean up previous stack, but the
check wasn't expecting this token. Fixes by adding skip for that token.

Resolves: #577
Signed-off-by: Arthur Zamarin <arthurzam@gentoo.org>

Author: arthurzam

src/pkgcheck/checks/profiles.py

@@ -278,7 +278,7 @@ def _use(self, filename, node, vals):
     )
     def _pkg_atoms(self, filename, node, vals):
         for x in iflatten_instance(vals, atom_cls):
-            if not self.search_repo.match(x):
+            if not isinstance(x, bool) and not self.search_repo.match(x):
                 yield UnknownProfilePackage(pjoin(node.name, filename), x)
 
     @verify_files(