[Rails5] Patch up exists? distinct 1 as one queries.

Author: metaskills

lib/arel/visitors/sqlserver.rb

@@ -170,7 +170,7 @@ def distinct_One_As_One_Is_So_Not_Fetch o
         core = o.cores.first
         distinct = Nodes::Distinct === core.set_quantifier
         oneasone = core.projections.all? { |x| x == ActiveRecord::FinderMethods::ONE_AS_ONE }
-        limitone = node_value(o.limit) == 1
+        limitone = [nil, 0, 1].include? node_value(o.limit)
         if distinct && oneasone && limitone && !o.offset
           core.projections = [Arel.sql("TOP(1) 1 AS [one]")]
           o.limit = nil