Disconnect resize observer after restoring initial page (#660)

Everytime the reader width got changed, the resize observer triggered the initial page to get scrolled into view again

src/components/reader/pager/HorizontalPager.tsx

@@ -115,6 +115,7 @@ export function HorizontalPager(props: IReaderProps) {
 
         const resizeObserver = new ResizeObserver(() => {
             initialPageElement.scrollIntoView({ inline: 'center' });
+            resizeObserver.disconnect();
         });
         resizeObserver.observe(initialPageElement);
 

src/components/reader/pager/VerticalPager.tsx

@@ -173,6 +173,7 @@ export function VerticalPager(props: IReaderProps) {
 
         const resizeObserver = new ResizeObserver(() => {
             initialPageElement.scrollIntoView();
+            resizeObserver.disconnect();
         });
         resizeObserver.observe(initialPageElement);