Handle a missing rack.input in the env

Ever since rack/rack#2018 `rack.input` has been
optional so we can't assume it's there and call `read` or `rewind` on it in
`Apipie::Extractor::Recorder`. Using safe navigation to call these methods
seems like the simplest approach because we want to look for
`rack.request.form_hash` instead in both the situation where `rack.input` is
missing, or it's empty.

lib/apipie/extractor/recorder.rb

@@ -14,12 +14,12 @@ def analyse_env(env)
         @params = Rack::Utils.parse_nested_query(@query)
         @params.merge!(env["action_dispatch.request.request_parameters"] || {})
         rack_input = env["rack.input"]
-        if data = parse_data(rack_input.read)
+        if data = parse_data(rack_input&.read)
           @request_data = data
         elsif form_hash = env["rack.request.form_hash"]
           @request_data = reformat_multipart_data(form_hash)
         end
-        rack_input.rewind
+        rack_input&.rewind
       end
 
       def analyse_controller(controller)