Try to parse command line argument as file names

… when parsing as an absolute URL (without a base) fails.

Previously, arguments were parsed as URLs with the current working directory
converted to an URL and used as the base URL. This mostly worked for
relative filenames, except that `?` and `#` had a special meaning
and needed to be percent-encoded.

Fix #3340.

tests/ref/basic.list

@@ -1,6 +1,7 @@
 == basic_width_px.html basic_width_em.html
 == br.html br-ref.html
-== hello_a.html hello_b.html
+# `?` and `#` in the name is a test for https://github.com/servo/servo/issues/3340
+== hello_a?foo#bar.html hello_b.html
 == margin_a.html margin_b.html
 == root_pseudo_a.html root_pseudo_b.html
 == first_child_pseudo_a.html first_child_pseudo_b.html