[LPDMini][Dark] Add only number of available data trains into data_samples

This is a fix for dark processing one of the runs related to this ticket https://redmine.xfel.eu/issues/153171 and https://in.xfel.eu/metadata/proposals/858#proposal-calibration (146, 147, and 148)

Description

In case the available dark data is less than ntrains this ValueError will be raised when adding data to data_samples. I have added this part to make sure we only add the available data trains.

How Has This Been Tested?

running LPDMINI dark processing for the failed run.

Relevant Documents (optional)

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

Reviewers

@kluyvert