ORBAT notes briefing requires marker colors even for groups without a marker

[darkChozo]

If you have an entry in groupData that doesn't specify a marker color, orbatNotes throws an error at line 50, even if a marker is not specified. This is inconsistent with the behavior of the group markers module.

Should be an easy fix; just resolve the marker color config later, and add in a check for whether the marker name is "" before adding the marker image.

repro: something like ["MyGroup","","","","Group - "] in groupData

[shadow-fa]

#268 also seems to have fixed this issue.