fix(replays): don't show jump down buttons if no scrolling is needed (#60055)

this was happening due to an off-by-one error. if we reach the end of
the replay and scroll to the bottom of the tab (e.g. the last
error/network/etc frame is visible), `rowIndex` is always 1 more than
the `visibleRange.stopIndex`. this was causing the button to render
again in this instance, which we don't want.

before:


https://github.com/getsentry/sentry/assets/56095982/1c619d60-c137-4340-a06c-261a3348a83b



after:


https://github.com/getsentry/sentry/assets/56095982/930917e7-5932-4727-b975-10a9cad955a5

fixes #58902

Author: michellewzhang

static/app/components/replays/useJumpButtons.tsx

@@ -57,7 +57,7 @@ export default function useJumpButtons({
     handleClick,
     onRowsRendered,
     onSectionRendered,
-    showJumpDownButton: rowIndex > visibleRange.stopIndex,
+    showJumpDownButton: rowIndex > visibleRange.stopIndex + 1,
     showJumpUpButton: rowIndex < visibleRange.startIndex,
   };
 }