iis: keep partial collector cleanup safe (#2605)

Signed-off-by: Jan-Otto Kröpke <mail@jkroepke.de>

internal/collector/iis/cache_metrics_test.go

@@ -133,3 +133,8 @@ func (f cacheFixture[T]) Collect(dst *[]T) error {
 }
 
 func (f cacheFixture[T]) Close() {}
+
+func TestCloseBeforeCacheProviderInitialization(t *testing.T) {
+	t.Parallel()
+	require.NoError(t, New(nil).Close())
+}

internal/collector/iis/iis.go

@@ -158,9 +158,16 @@ func (c *Collector) Close() error {
 	c.perfDataCollectorWebService.Close()
 	c.perfDataCollectorHttpServiceRequestQueues.Close()
 	c.perfDataCollectorAppPoolWAS.Close()
-	c.w3SVCW3WPPerfDataCollector.Close()
+
+	if c.w3SVCW3WPPerfDataCollector != nil {
+		c.w3SVCW3WPPerfDataCollector.Close()
+	}
+
 	c.w3SVCW3WPPerfDataCollectorV8.Close()
-	c.serviceCachePerfDataCollector.Close()
+
+	if c.serviceCachePerfDataCollector != nil {
+		c.serviceCachePerfDataCollector.Close()
+	}
 
 	return nil
 }