Rewind IO-alike request body after it was consumed.

Webmock triggers `body.each` twice upon inital request recording:

1. to perform request
2. to record request data into webmock request registry

But even without WebMock, generally Body#each must be replayable IMO.

lib/http/request/body.rb

@@ -35,6 +35,7 @@ def each(&block)
           yield @source
         elsif @source.respond_to?(:read)
           IO.copy_stream(@source, ProcIO.new(block))
+          @source.rewind if @source.respond_to?(:rewind)
         elsif @source.is_a?(Enumerable)
           @source.each(&block)
         end