Checking error in the select_old module when (#180)

Checking error in the select_old module when
receiving iterator is now called earlier than
checking tuple. Closes #144

Author: mRrvz

crud/select/compat/select_old.lua

@@ -218,14 +218,14 @@ function select_module.pairs(space_name, user_conditions, opts)
 
     local gen = function(_, iter)
         local tuple, err = iter:get()
-        if tuple == nil then
-            return nil
-        end
-
         if err ~= nil then
             error(string.format("Failed to get next object: %s", err))
         end
 
+        if tuple == nil then
+            return nil
+        end
+
         local result = tuple
         if opts.use_tomap == true then
             result, err = utils.unflatten(tuple, iter.space_format)