fix latestSpanEndTimestamp calc

Author: Lms24

packages/core/src/tracing/idleSpan.ts

@@ -171,10 +171,10 @@ export function startIdleSpan(startSpanOptions: StartSpanOptions, options: Parti
       // Otherwise, we adjust the end timestamp of the idle span to the latest span end timestamp of its children
       const latestSpanEndTimestamp = spans?.reduce((acc: number | undefined, current) => {
         const currentSpanJson = spanToJSON(current);
-        if (acc == null) {
-          return currentSpanJson.timestamp;
+        if (!currentSpanJson.timestamp) {
+          return acc;
         }
-        return Math.max(acc, currentSpanJson.timestamp || 0);
+        return acc ? Math.max(acc, currentSpanJson.timestamp) : currentSpanJson.timestamp;
       }, undefined);
 
       // In reality this should always exist here, but type-wise it may be undefined...