tcp: fix panic on collector (#1699)

internal/collector/tcp/tcp_test.go

@@ -10,3 +10,7 @@ import (
 func BenchmarkCollector(b *testing.B) {
 	testutils.FuncBenchmarkCollector(b, tcp.Name, tcp.NewWithFlags)
 }
+
+func TestCollector(t *testing.T) {
+	testutils.TestCollector(t, tcp.New, nil)
+}

internal/perfdata/v1/collector.go

@@ -44,7 +44,7 @@ func (c *Collector) Collect() (map[string]map[string]perftypes.CounterValues, er
 		return nil, fmt.Errorf("QueryPerformanceData: %w", err)
 	}
 
-	if len(perfObjects) == 0 {
+	if len(perfObjects) == 0 || perfObjects[0] == nil || len(perfObjects[0].Instances) == 0 {
 		return map[string]map[string]perftypes.CounterValues{}, nil
 	}
 

internal/perfdata/v1/perflib.go

@@ -418,6 +418,10 @@ func QueryPerformanceData(query string, counterName string) ([]*PerfObject, erro
 			}
 		}
 
+		if counterName != "" {
+			return objects[i : i+1], nil
+		}
+
 		// Next perfObjectType
 		objOffset += int64(obj.TotalByteLength)
 		numFilteredObjects++