Properly check if document is loaded, closes #2716

Editor assessment

The subject states the remedy with a filler adverb: the document-loaded check is now properly performed, with a meaningful core scope and a well-formed closes #2716 footer. The word properly concedes prior misbehavior without characterizing it, whether events fired early or readiness was assumed, so the defect itself is never described. The fix type is right, no body exists to explain the race or the corrected gating, and no additional footers appear. Hygiene is acceptable. The message ties the change to its issue but communicates little on its own.