Allow clean-ignore to run without arguments.

Signed-off-by: Connor E. Basile <cbasile2@gmail.com>

contrib/filter-repo-demos/clean-ignore

@@ -69,7 +69,10 @@ class CheckIgnores:
 
 def main():
   checker = CheckIgnores()
-  args = fr.FilteringOptions.parse_args(sys.argv[1:])
+  if sys.argsv[1:]:
+    args = fr.FilteringOptions.parse_args(sys.argv[1:])
+  else:
+    args = fr.FilteringOptions.parse_args(['--force'])
   filter = fr.RepoFilter(args, commit_callback=checker.skip_ignores)
   filter.run()