BUG#32413458 FIXES ARITHMETIC EXCEPTION IN NDB_INIT

Fixes arithmetic exception when trying to calculate the amount of
instructions to pause cpu using spinning (introduced in WL#12554).

Under some situations, when trying to measure the time of a cpu pause,
we might end up with an elapsed time of zero (e.g. non-monotonic clock).
Also, if spinning is really fast (100 loops taking less than 100ns) we
might compute an average of zero nanoseconds.
In both cases, this will cause the algorithm to calibrate spinning to
throw an arithmetic exception due to division by zero.

Modifies the algorithm to ignore zero values when computing mean
spinning time.

Change-Id: I55166705e1a0d5fa453aa2a75831db8943321541

Author: Tiago Alves

storage/ndb/src/common/portlib/NdbSpin.cpp

@@ -50,11 +50,12 @@ void NdbSpin_Init()
     NDB_TICKS now = NdbTick_getCurrentTicks();
     const Uint64 nanos_passed = NdbTick_Elapsed(start, now).nanoSec();
     const Uint64 nanos_per_call = nanos_passed / loop_count;
-    if (nanos_per_call < min_nanos_per_call)
+    if ((nanos_per_call > 0) && (nanos_per_call < min_nanos_per_call))
     {
       min_nanos_per_call = nanos_per_call;
     }
   }
+
   loops = ((min_nanos_per_call - 1) + spin_nanos) / min_nanos_per_call;
 #endif
   if (loops == 0)