fix(honeycomb-opentelemetry-web): Add check for lcpEntry.element (#342)

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## Which problem is this PR solving?
Sometimes `lcpEntry.element` is null or undefined, this check prevents
an `Cannot read properties of undefined (reading 'dataset')` error.

## How to verify that this has the expected result

packages/honeycomb-opentelemetry-web/src/web-vitals-autoinstrumentation.ts

@@ -483,7 +483,7 @@ export class WebVitalsInstrumentation extends InstrumentationAbstract {
     });
 
     const el: HTMLElement = lcpEntry?.element as HTMLElement;
-    if (el.dataset) {
+    if (el?.dataset) {
       for (const attrName in el.dataset) {
         const attrValue = el.dataset[attrName];
         if (