Fix crash when a view destroys with pending transactions
Fix crash when a view destroys with pending transactions

We were removing the saved buffer when one transaction applies, then
didn't have a new buffer to save when the next transaction ran. This
made the rendering code crash as it had no surface to use.

This commit makes it continue to hold the buffer if the view is
destroying and has more transactions. Additionally, a check is added
when saving the buffer to make sure there's no one already there.

1ace/sway,ascent12/sway,1ace/sway,ascent12/sway,ascent12/sway,1ace/sway,taiyu-len/sway,taiyu-len/sway,SirCmpwn/sway,taiyu-len/sway