Respect the current connected? method when calling cache

Before we enable query caching we check if the connection is
connected. Before this fix we were always checking against the main
connection, and not the model connection.

activerecord/lib/active_record/query_cache.rb

@@ -5,7 +5,7 @@ module ClassMethods
       # Enable the query cache within the block if Active Record is configured.
       # If it's not, it will execute the given block.
       def cache(&block)
-        if ActiveRecord::Base.connected?
+        if connected?
           connection.cache(&block)
         else
           yield
@@ -15,7 +15,7 @@ def cache(&block)
       # Disable the query cache within the block if Active Record is configured.
       # If it's not, it will execute the given block.
       def uncached(&block)
-        if ActiveRecord::Base.connected?
+        if connected?
           connection.uncached(&block)
         else
           yield

activerecord/test/cases/query_cache_test.rb

@@ -174,6 +174,21 @@ def test_cache_is_available_when_connection_is_connected
     ActiveRecord::Base.configurations = conf
   end
 
+  def test_cache_is_not_available_when_using_a_not_connected_connection
+    spec_name = Task.connection_specification_name
+    conf = ActiveRecord::Base.configurations['arunit'].merge('name' => 'test2')
+    ActiveRecord::Base.connection_handler.establish_connection(conf)
+    Task.connection_specification_name = "test2"
+    refute Task.connected?
+
+    Task.cache do
+      assert_queries(2) { Task.find(1); Task.find(1) }
+    end
+  ensure
+    ActiveRecord::Base.connection_handler.remove_connection(Task.connection_specification_name)
+    Task.connection_specification_name = spec_name
+  end
+
   def test_query_cache_doesnt_leak_cached_results_of_rolled_back_queries
     ActiveRecord::Base.connection.enable_query_cache!
     post = Post.first