when a variant is empty do not add it to the repolist for livemedia

Signed-off-by: Dennis Gilmore <dennis@ausil.us>

pungi/phases/livemedia_phase.py

@@ -40,7 +40,8 @@ class LiveMediaPhase(PhaseBase):
         repo = shortcuts.force_list(image_conf.get('repo', []))
 
         extras = shortcuts.force_list(image_conf.pop('repo_from', []))
-        extras.append(variant.uid)
+        if not variant.is_empty:
+            extras.append(variant.uid)
 
         for extra in extras:
             v = self.compose.variants.get(extra)