fix(tracing): Add an extra conditional check to web vitals onCLS()

Author: timfish

packages/tracing/src/browser/web-vitals/getCLS.ts

@@ -61,6 +61,7 @@ export const onCLS = (onReport: ReportCallback, opts: ReportOpts = {}): void =>
         // entry in the current session. Otherwise, start a new session.
         if (
           sessionValue &&
+          sessionEntries.length !== 0 &&
           entry.startTime - lastSessionEntry.startTime < 1000 &&
           entry.startTime - firstSessionEntry.startTime < 5000
         ) {