[PNCCD][CORRECT] Fix: Skip error for missing gain

This MR is on top of !842 (closed)

Description

This MR didn't achieve what it was supposed to !837 (merged) for avoiding errors when only the gain constants were not retrieved for pnccd.

Here I change the order for some lines to write fragments before reading constant data. Also removing the unneeded try/except as the CCVError is not caught at !842 (closed)

How Has This Been Tested?

Running jupyter notebook interactively.

Relevant Documents (optional)

Types of changes

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

Checklist:

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