fix davidbiehl#6

Made this changes, as @aleccarper suggested [here](davidbiehl#6 (comment))
I was encountering those issue quite often while using this gem on my production app, @davidbiehl also asked for pull request, so I made it

lib/ecwid_api/paged_ecwid_response.rb

@@ -36,13 +36,16 @@ def initialize(client, path, params = {}, &block)
       response = client.get(path, params)
 
       @paged_enumerator = PagedEnumerator.new(response) do |response, yielder|
-        response.body["items"].each do |item|
-          yielder << block.call(item)
-        end
-
+
         count, offset, total = %w(count offset total).map do |i|
           response.body[i].to_i
         end
+
+        if count > 0
+          response.body["items"].each do |item|
+            yielder << block.call(item)
+          end
+        end  
 
         if count == 0 || count + offset >= total
           false
@@ -52,4 +55,4 @@ def initialize(client, path, params = {}, &block)
       end
     end
   end
-end
+end