Fix iterator for issue #2438.

Itereator misuse due to analyzeLatencyForEvent() accessing the
dictionary during the iteration, without the iterator being
reclared as safe.

src/latency.c

@@ -247,7 +247,7 @@ sds createLatencyReport(void) {
     dictEntry *de;
     int eventnum = 0;
 
-    di = dictGetIterator(server.latency_events);
+    di = dictGetSafeIterator(server.latency_events);
     while((de = dictNext(di)) != NULL) {
         char *event = dictGetKey(de);
         struct latencyTimeSeries *ts = dictGetVal(de);