If the stack overflow trap region has already been tripped, don't continue to ignore faults there.

In the unlikely case that it tripped and then, due to a bug, some other
fault occurred (e.g. stack misalignment), Dolphin would go into an
infinite loop rather than crashing.
Merge pull request #1299 from comex/blr-opt-infinite-loop

If the stack overflow trap region has already been tripped, don't continue to ignore faults there.