csv.rb: fix field_size_limit check

* lib/csv.rb (CSV#shift): the last column is an Array in extended
  column since r55985.  [ruby-dev:49964] [Bug #13149]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57406 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/csv/test_csv_parsing.rb

@@ -209,6 +209,28 @@ class TestCSV::Parsing < TestCSV
                              field_size_limit: 2048 )
   end
 
+  def test_field_size_limit_in_extended_column_not_exceeding
+    data = <<~DATA
+      "a","b"
+      "
+      2
+      ",""
+    DATA
+    assert_nothing_raised(CSV::MalformedCSVError) do
+      CSV.parse(data, field_size_limit: 4)
+    end
+  end
+
+  def test_field_size_limit_in_extended_column_exceeding
+    data = <<~DATA
+      "a","b"
+      "
+      2345
+      ",""
+    DATA
+    assert_parse_errors_out(data, field_size_limit: 5)
+  end
+
   private
 
   def assert_parse_errors_out(*args)