ART: Fix critical edge splitting under try/catch

A critical edge would not be split if the predecessor ends with
TryBoundary. This would eventually trip liveness analysis because
a back edge block would have smaller liveness position than a nested
loop.

Another implication of this change is that an edge between a loop's
pre-header ending with TryBoundary and the header will be split,
guaranteeing that a pre-header always has just one successor.

Bug: 25493695
Bug: 25454012
Change-Id: I5a13b8bb74509b48f5d628906f7158af007f99ae