Fix a bug in the itimer sample source.  The combination of MPI plus HPCRUN_DELAY_SAMPLING (hpcrun -ds) plus REALTIME or CPUTIME event produced a code path where the timerid is uninitialized, leading to a segfault in hpcrun_stop_timer().
Fix a bug in the itimer sample source.  The combination of MPI plus
HPCRUN_DELAY_SAMPLING (hpcrun -ds) plus REALTIME or CPUTIME event
produced a code path where the timerid is uninitialized, leading to a
segfault in hpcrun_stop_timer().

This bug affects REALTIME and CPUTIME but not WALLCLOCK because the
POSIX timers need an extra step to create the timer that setitimer()
doesn't use.

HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit,zcth428/hpctoolkit,HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit,zcth428/hpctoolkit,zcth428/hpctoolkit,zcth428/hpctoolkit,zcth428/hpctoolkit,HPCToolkit/hpctoolkit