Do not stop FdEventsReader on handlePacket error

Previously if handlePacket threw an exception, FdEventsReader would
stop reading and close the file descriptor.
This is not helpful as users of this class may encounter errors
processing a particular packet (typically), but they generally should
not stop completely for that reason.

Also address comments from previous change (Exception instead of
Throwable: Throwable should not be caught in general; event -> events).

Bug: 152842850
Test: atest NetworkStackTests
Original-Change: https://android-review.googlesource.com/1295503
Merged-In: I14abe8163ecdfd5251731915f10ea374bfa38b70
Change-Id: I14abe8163ecdfd5251731915f10ea374bfa38b70