Don't invoke response block more than once due to retry

If a socket error occurs while performing a streaming download via
the response block provided to transport_request, avoid calling
the response block again as this would result in duplicate data
received by the client.

Fixes #86
Fixes #87 

Fixes [Bug #11526]

Co-authored-by: Jeremy Stanley <jeremy@instructure.com>

lib/net/http.rb

@@ -2350,7 +2350,10 @@ def transport_request(req)
           res
         }
         res.reading_body(@socket, req.response_body_permitted?) {
-          yield res if block_given?
+          if block_given?
+            count = max_retries # Don't restart in the middle of a download
+            yield res
+          end
         }
       rescue Net::OpenTimeout
         raise

test/net/http/test_http.rb

@@ -1234,6 +1234,16 @@ def test_http_retry_failed
     }
   end
 
+  def test_http_retry_failed_with_block
+    start {|http|
+      http.max_retries = 10
+      called = 0
+      assert_raise(Errno::ECONNRESET){ http.get('/'){called += 1; raise Errno::ECONNRESET} }
+      assert_equal 1, called
+    }
+    @log_tester = nil
+  end
+
   def test_keep_alive_server_close
     def @server.run(sock)
       sock.close