Repair `generate-codebook` display logic

[nmdefries]

generate-codebook doesn't create display logic field correctly when the display logic does not depend on a question. The main use case for this is when we suppress questions from being shown to any respondent, e.g.

Display logic info for item V2 in QSF for Wave 12 (final version):

"Description": "<span class=\"ConjDesc\">If</span><span> False</span>",
"LogicType": "BooleanValue",
"Type": "Expression",
"Value": "False"

The codebook script interprets this as "If ". It should be "If False".