fix(AGIPD)(CORRECT): bug when plotting gain data of only 0 after it's info was discarded by DAQ

Description

Fix for this issue and ticket

This is already hotfixed in production by Thomas K.

How Has This Been Tested?

Relevant Documents (optional)

Types of changes

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

Checklist:

Reviewers

@kluyvert @schmidtp