update_with_password doesn't change encrypted password when it is invalid

closes #2130

lib/devise/models/database_authenticatable.rb

@@ -64,6 +64,7 @@ module Devise
         result = if valid_password?(current_password)
           update_attributes(params, *options)
         else
+          params.delete(:password)
           self.assign_attributes(params, *options)
           self.valid?
           self.errors.add(:current_password, current_password.blank? ? :blank : :invalid)