#673 Choose 'Enable NTP',no value in webgui 'port' save will fail

[skygunner]

If choose 'Enable NTP',
but webgui section 'port' hasn't been edited and saved before, save will fail with error code 1.

For example, check fresh install, check 'Enable NTP' and save, will have this error.
Only give a port number in 'port' will successfully save it.
If once saved successfully, whether there's value or empty in 'port', save will success.

Tested in 4735 4787 4888 i386 embedded