Fix#4099. Ods Reader was expecting there to always be `header-style` and `footer-style` tags when `page-layout` tag is present, but these need not exist. It seemed like there might be other exposures along this line in `readPageSettingStyles`; rather than waiting for a problem report to show up for each, the code is updated to use `->item(0)` in place of `[0]` when appropriate, and make use of the nullsafe `?->` operator introduced with Php8.
oleibman