Recreate transient pendingAccessQueue in readObject() (#12456)

This prevents a race condition in getPendingAccessQueue().

Change-Id: I1b8d013119e5963ed6083b7dd17afccd3a915e42
Merge commit 'ebdc3652764e8ec2ce292879d459a8d0c6c2d2e3'

Conflicts:
	server/src/com/vaadin/server/VaadinSession.java

Change-Id: I51383060a95354b7ffbcc5b12683c1d1a817b8bf