Default grid intensities not returned when only setting some segments in perVisitTrace

[APJohns]

Describe the bug
When only providing one segment to gridIntensity in perVisitTrace, the returned variables.gridIntensity only shows what was provided and no longer shows the default global intensity for the other segments.

To Reproduce
Steps to reproduce the behavior:

1. Call perVisitTrace using SWD model while only providing one or two segment grid intensities
2. Notice returned variables.gridIntensities only contains the ones you set

Expected behavior
Returned variables.gridIntensity should show all intensities (including defaults).

Environment (please complete the following information):

• NodeJS

[fershad]

@APJohns thanks for this. I've seen your PR too. I'll have a look at these on Friday this week when I've got a bit more bandwidth.