fix(browser): guard nextHopProtocol when adding resource spans (#16900)

ref #16804

This was addressed with
#16806, but we didn't
guard every location that uses `entry.nextHopProtocol`.

Will backport to v9 after merge.

---------

Co-authored-by: Lukas Stracke <lukas.stracke@sentry.io>

Author: AbhiPrasad

packages/browser-utils/src/metrics/browserMetrics.ts

@@ -715,9 +715,13 @@ export function _addResourceSpans(
 
   attributes['url.same_origin'] = resourceUrl.includes(WINDOW.location.origin);
 
-  const { name, version } = extractNetworkProtocol(entry.nextHopProtocol);
-  attributes['network.protocol.name'] = name;
-  attributes['network.protocol.version'] = version;
+  // Checking for only `undefined` and `null` is intentional because it's
+  // valid for `nextHopProtocol` to be an empty string.
+  if (entry.nextHopProtocol != null) {
+    const { name, version } = extractNetworkProtocol(entry.nextHopProtocol);
+    attributes['network.protocol.name'] = name;
+    attributes['network.protocol.version'] = version;
+  }
 
   const startTimestamp = timeOrigin + startTime;
   const endTimestamp = startTimestamp + duration;