Handle l param missing for WKD request

spec/requests/web_key_directory_spec.rb

@@ -9,6 +9,13 @@ RSpec.describe "OpenPGP Web Key Directory", type: :request do
     end
   end
 
+  describe "omitted 'l' param" do
+    it "returns a 404 status" do
+      get "/.well-known/openpgpkey/hu/fmb8gw3n4zdj4xpwaziki4mwcxr1368i"
+      expect(response).to have_http_status(:not_found)
+    end
+  end
+
   describe "non-existent user" do
     it "returns a 404 status" do
       get "/.well-known/openpgpkey/hu/fmb8gw3n4zdj4xpwaziki4mwcxr1368i?l=aristotle"