Added test to ensure that we dont break #to_h again when trying to restore the...

Added test to ensure that we dont break #to_h again when trying to restore the speed-up from 26dd9b26 (cc: @fxn)

actionpack/test/controller/parameters/nested_parameters_permit_test.rb

@@ -140,6 +140,11 @@ def assert_filtered_out(params, key)
     assert_equal "William Shakespeare", permitted[:book][:authors_attributes]["0"][:name]
     assert_equal "Unattributed Assistant", permitted[:book][:authors_attributes]["1"][:name]
 
+    assert_equal(
+      {"book"=>{"authors_attributes"=>{"0"=>{"name"=>"William Shakespeare"}, "1"=>{"name"=>"Unattributed Assistant"}, "2"=>{}}}}, 
+      permitted.to_h
+    )
+
     assert_filtered_out permitted[:book][:authors_attributes]["0"], :age_of_death
   end