Allow empty path in url.parse.

I got a redirect of "?p=indisponible" and url.parse returned
{query="p=indisponible"}. Now it returns
{path="", query="p=indisponible"}.

nselib/url.lua

@@ -178,7 +178,7 @@ function parse(url, default)
         return ""
     end)
     -- path is whatever was left
-    if url ~= "" then parsed.path = url end
+    parsed.path = url
     local authority = parsed.authority
     if not authority then return parsed end
     authority = string.gsub(authority,"^([^@]*)@",