Fix scroll gesture alignment (#6898)

src/view/com/util/MainScrollProvider.tsx

···
   const snapToClosestState = useCallback(
     (e: NativeScrollEvent) => {
       'worklet'
+      const offsetY = Math.max(0, e.contentOffset.y)
       if (isNative) {
         const startDragOffsetValue = startDragOffset.get()
         if (startDragOffsetValue === null) {
           return
         }
-        const didScrollDown = e.contentOffset.y > startDragOffsetValue
+        const didScrollDown = offsetY > startDragOffsetValue
         startDragOffset.set(null)
         startMode.set(null)
-        if (e.contentOffset.y < headerHeight.get()) {
+        if (offsetY < headerHeight.get()) {
           // If we're close to the top, show the shell.
           setMode(false)
         } else if (didScrollDown) {
···
   const onBeginDrag = useCallback(
     (e: NativeScrollEvent) => {
       'worklet'
+      const offsetY = Math.max(0, e.contentOffset.y)
       if (isNative) {
-        startDragOffset.set(e.contentOffset.y)
+        startDragOffset.set(offsetY)
         startMode.set(headerMode.get())
       }
     },
···
   const onScroll = useCallback(
     (e: NativeScrollEvent) => {
       'worklet'
+      const offsetY = Math.max(0, e.contentOffset.y)
       if (isNative) {
         const startDragOffsetValue = startDragOffset.get()
         const startModeValue = startMode.get()
         if (startDragOffsetValue === null || startModeValue === null) {
-          if (
-            headerMode.get() !== 0 &&
-            e.contentOffset.y < headerHeight.get()
-          ) {
+          if (headerMode.get() !== 0 && offsetY < headerHeight.get()) {
             // If we're close enough to the top, always show the shell.
             // Even if we're not dragging.
             setMode(false)
···
 
         // The "mode" value is always between 0 and 1.
         // Figure out how much to move it based on the current dragged distance.
-        const dy = e.contentOffset.y - startDragOffsetValue
+        const dy = offsetY - startDragOffsetValue
         const dProgress = interpolate(
           dy,
           [-headerHeight.get(), headerHeight.get()],
···
         }
         // On the web, we don't try to follow the drag because we don't know when it ends.
         // Instead, show/hide immediately based on whether we're scrolling up or down.
-        const dy = e.contentOffset.y - (startDragOffset.get() ?? 0)
-        startDragOffset.set(e.contentOffset.y)
+        const dy = offsetY - (startDragOffset.get() ?? 0)
+        startDragOffset.set(offsetY)
 
-        if (dy < 0 || e.contentOffset.y < WEB_HIDE_SHELL_THRESHOLD) {
+        if (dy < 0 || offsetY < WEB_HIDE_SHELL_THRESHOLD) {
           setMode(false)
         } else if (dy > 0) {
           setMode(true)