Fixed swallower access. Now error handler logs exceptions. (#12703)

Change-Id: If8fe00e10c7ec56cbd8753ff88d4816613a340f2
Merge commit 'd461fb438f62b38d2082b41b0a3c7a1189927c3d'

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

Change-Id: Ieac9cce1d3a0351d21d433e523f2ab8e97550f50