libmojo: Add one more callback exception handler

Upon further inspection, there is one more callback invocation site
where we want to handle exceptions from.

Bug: 28986534
Bug: 64805573
Bug: 73005146
Test: m

Change-Id: I021ff2111e000eee4e9242afd87ad3b4420f6119
Merged-In: I021ff2111e000eee4e9242afd87ad3b4420f6119
(cherry picked from commit 41ea301886adf58cb6eb7aef138cc344af875ef9)