keep ref value locally

Author: fandreuz

sdk/metrics/src/main/java/io/opentelemetry/sdk/metrics/internal/state/SdkObservableMeasurement.java

@@ -101,6 +101,7 @@ public void record(long value) {
 
   @Override
   public void record(long value, Attributes attributes) {
+    RegisteredReader activeReader = this.activeReader;
     if (activeReader == null) {
       logNoActiveReader();
       return;