test_qthelpplugin: don't crash after running for >= 60 seconds
All 12 qthelpplugin test cases pass on my computer, but occasionally (when some Qt Help database is updated?) they run for slightly longer than a minute. Thus an occasional crash on exit.
Such a crash in test_gdbprinters was worked around in the same way in efff8aff. For some reason the received signal is now SegFault instead of SIGPIPE.