JSO dispatch in JSNI was only sometimes blocked, fixed.

The enforcement of blocking JSO dispatch in JSNI depended on a
datastructure that was not guarranteed to yet be fully populated.

Moved the enforcement to a later compiler stage.

Change-Id: I5867ef061a36095e1393e06e289d6cc2e1e1e692
(cherry picked from commit 0a62bc72ba32ab832ab8dabe939cf839f03439e7)