ZeroJankProxy: Fix system_server crash when on bad app calls.

Fixes an issue where system_server would crash if an exception
gets thrown, now that those no longer get thrown back
at the application.

Fixes: 327975111
Test: atest com.android.server.inputmethod.InputMethodManagerServiceWindowGainedFocusTest
Change-Id: I008198157424c544d4973eb94434b458e27f15fd