Fix exception when time zone of browser unavailable

apps/client/src/app/core/auth.interceptor.ts

@@ -38,10 +38,13 @@ export class AuthInterceptor implements HttpInterceptor {
       return next.handle(request);
     }
 
-    let headers = request.headers.set(
+    let headers = request.headers;
-      HEADER_KEY_TIMEZONE,
+
-      Intl?.DateTimeFormat().resolvedOptions().timeZone
+    const timezone = Intl.DateTimeFormat().resolvedOptions().timeZone;
-    );
+
+    if (timezone) {
+      headers = headers.set(HEADER_KEY_TIMEZONE, timezone);
+    }
 
     const token = this.tokenStorageService.getToken();