"Grab after a delay of..." is disabled for "Select area to grab" (`mate-screenshot -i`)

[Norbert]

Steps to reproduce:
1. Launch mate-screenshot interactively with `mate-screenshot -i`
2. Click on "Select are to grab" for taking screenshot of area
3. Try to set delay

Expected results:
User is able to set delay when creating screenshot of area

Actual results:
User is unable to set delay when creating screenshot of area - it is disabled.

First seen on AskUbuntu (https://askubuntu.com/q/1008771/66509).

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: mate-utils 1.12.0-1
ProcVersionSignature: Ubuntu 4.4.0-112.135-generic 4.4.98
Uname: Linux 4.4.0-112-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.15
Architecture: amd64
CurrentDesktop: MATE
Date: Fri Feb 23 13:21:43 2018
InstallationDate: Installed on 2018-01-04 (49 days ago)
InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
SourcePackage: mate-utils
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Sai Vinoba (saivinob)]

Do we need the ability to set delay for 'Select area to grab' option? Isn't the delay inherent, in the sense, the cross-hair is on waiting for us to drag over an area and release the mouse button?