Fix accordion startOpen behaviour if Phy's audience calculation undefined

Author: jacbn

src/app/components/content/IsaacAccordion.tsx

@@ -183,7 +183,8 @@ export const IsaacAccordion = ({doc}: {doc: ContentDTO}) => {
                 {isPhy && stageInserts?.[index] && <StageInsert stage={stageInserts[index]} />}
                 <Accordion
                     key={`${section.sectionIndex} ${index}`} id={section.id} index={index}
-                    startOpen={section.startOpen || index === firstSectionToOpen} deEmphasised={section.deEmphasised}
+                    startOpen={section.startOpen || !isDefined(firstSectionToOpen) ? undefined : index === firstSectionToOpen} /* use default <Accordion/> startOpen behaviour if behaviour undefined */
+                    deEmphasised={section.deEmphasised}
                     trustedTitle={section?.title || ""}
                     audienceString={audienceString}
                 >