DEV: allow handling crawler reqs with no user agent

Followup to e440ec25 we treat no user agent as crawler reqs.

lib/middleware/request_tracker.rb

@@ -118,7 +118,7 @@ class Middleware::RequestTracker
 
     if h[:is_crawler]
       user_agent = env['HTTP_USER_AGENT']
-      if user_agent.encoding != Encoding::UTF_8
+      if user_agent && (user_agent.encoding != Encoding::UTF_8)
         user_agent = user_agent.encode("utf-8")
         user_agent.scrub!
       end

spec/components/hijack_spec.rb

@@ -65,7 +65,6 @@ describe Hijack do
 
       expect(@calls).to eq(1)
       expect(@status).to eq(201)
-      expect(@status).to be > 0
     end
   end