Open previous chapter transition page in double page mode

For the double page mode the secondary page index gets used.
This was changed with 9a8655db2f, however, this occurrence was overlooked

src/modules/reader/services/ReaderControls.ts

@@ -261,7 +261,7 @@ export class ReaderControls {
         const indexOfLastPage = getNextIndexFromPage(pages[pages.length - 1]);
         const direction = READING_DIRECTION_TO_THEME_DIRECTION[readingDirection.value];
 
-        const isFirstPage = currentPageIndex === 0;
+        const isFirstPage = currentPage.primary.index === 0;
         const isLastPage = currentPageIndex === indexOfLastPage;
         const isATransitionPageVisible = transitionPageMode !== ReaderTransitionPageMode.NONE;
         const isContinuousReadingModeActive = isContinuousReadingMode(readingMode.value);