bugfix: fixing clogged connection requests after a jumbo one

In an already initiated connection, when piping multiple requests to be
sent concurrently, a case happened where the first filled the write
buffer, leaving the second in the connection pending queue; the initial
request would finish without ever taking the subsequent request from the
pending queue, leaving the connection hanging.

this was fixed by making flushing the queue part of the #consume work.

lib/httpx/connection.rb

@@ -362,6 +362,8 @@ module HTTPX
             write_drained = false
           end unless interests == :r
 
+          send_pending if @state == :open
+
           # return if socket is drained
           next unless (interests != :r || read_drained) &&
                       (interests != :w || write_drained)