title: tiny_tds row count (affected_rows) not working
body: <p>Perhaps I misunderstand how to get a count of rows returned by tiny_tds, which talks to ms sql server.</p>
  
  <p>The following code produces -1 rows</p>
  
  <pre><code> sql = "EXEC [Arrivals] @startDate='#{@startDate}', @endDate='#{@endDate}'"
   client = TinyTds::Client.new(...)
   result = client.execute(sql)
   result.each
   p result.affected_rows   (always returns -1)
  </code></pre>
  
  <p>This code, using a loop, counts rows correctly:</p>
  
  <pre><code> sql = "EXEC [Arrivals] @startDate='#{@startDate}', @endDate='#{@endDate}'"
   client = TinyTds::Client.new(...)
   result = client.execute(sql)
   @no_of_arrivals = 0
   result.each do |row|
     @no_of_arrivals = @no_of_arrivals  + 1
   end
   p @no_of_arrivals    (returns correct count)
  </code></pre>
  
  <p>I did see affected_rows in action earlier today, on a table, and it worked.  Could it have something to do with the SP... am I missing something obvious?</p>