Check for refocus also during the calibration stage

Summary:
In the Capture module there is an option to re-focus every x minutes. The check whether the selected time has expired, takes place after an image has been taken and there is anotherone in the same sequence. Sequences, that contain only single frames (like a single LRGB sequence) result in the situation, that re-focussing is never started.
To cover such sequences, it is necessary to check before an imaging sequence is started, whether a re-focus is necessary.

Test Plan: Create a capture sequence with a single frame and embed it into a schedule that repeatedly starts it. Select the re-focus option and set the frequency to 1. Without this patch, re-focusing will never be issued. With this patch, re-focusing takes place as expected.

Reviewers: mutlaqja, TallFurryMan

Reviewed By: mutlaqja, TallFurryMan

Subscribers: kde-edu

Tags: KDE Edu

Differential Revision: https://phabricator.kde.org/D22437