Long text custom fields don't accept values longer than 64KB if backend database is MySQL (#29209).

git-svn-id: https://svn.redmine.org/redmine/trunk@17965 e93f8b46-1217-0410-a6f0-8f06a7374b81

db/migrate/20190315094151_change_custom_values_value_limit.rb

+class ChangeCustomValuesValueLimit < ActiveRecord::Migration[5.2]
+  def up
+    if ActiveRecord::Base.connection.adapter_name =~ /mysql/i
+      max_size = 16.megabytes
+      change_column :custom_values, :value, :text, :limit => max_size
+    end
+  end
+
+  def down
+    # no-op
+  end
+end