If win stat buffer is empty, do not try to index

closes #1425

CHANGELOG.md

@@ -126,6 +126,7 @@ consistent with the behavior of `collection_jitter`.
 - [#1322](https://github.com/influxdata/telegraf/issues/1322): Fix rare RHEL 5.2 panic in gopsutil diskio gathering function.
 - [#1586](https://github.com/influxdata/telegraf/pull/1586): Remove IF NOT EXISTS from influxdb output database creation.
 - [#1600](https://github.com/influxdata/telegraf/issues/1600): Fix quoting with text values in postgresql_extensible plugin.
+- [#1425](https://github.com/influxdata/telegraf/issues/1425): Fix win_perf_counter "index out of range" panic.
 
 ## v0.13.1 [2016-05-24]
 

plugins/inputs/win_perf_counters/win_perf_counters.go

@@ -272,6 +272,9 @@ func (m *Win_PerfCounters) Gather(acc telegraf.Accumulator) error {
 				&bufCount, &emptyBuf[0]) // uses null ptr here according to MSDN.
 			if ret == win.PDH_MORE_DATA {
 				filledBuf := make([]win.PDH_FMT_COUNTERVALUE_ITEM_DOUBLE, bufCount*size)
+				if len(filledBuf) == 0 {
+					continue
+				}
 				ret = win.PdhGetFormattedCounterArrayDouble(metric.counterHandle,
 					&bufSize, &bufCount, &filledBuf[0])
 				for i := 0; i < int(bufCount); i++ {