This commit sets the initial scroll offset to the pinning offset.
The previous implementation, which set it to the current content offset,
leads various scroll tracking bugs. This reproduction is one of issues.
Using 'Scroll tracking(UITableView)' in Samples app.
1. Bounce the scroll content at the top most anchor.
2. Pull down the panel in bouncing at a minus content offset. (the
scroll content stops at the minus offset.)
3. Pull up it
The previous implementation was implemented for #526/#527. But now the
issue hasn't been reproduced in v2.5.6.
Shin Yamamoto
f92279484f