Increase sleep time to retrieve chairs emails

The CDN in front of W3C servers seems to have become more picky over rate
limits and rejects requests that are chained too fast. Making the code sleep
4s in between requests seems to solve the issue (but makes the script take
a long long time :().

tools/list-chairs.mjs

@@ -78,15 +78,20 @@ async function main(format) {
           await authenticate(page, W3C_LOGIN, W3C_PASSWORD, url);
           chair.email = await page.evaluate(() => {
             const el = document.querySelector('.card--user a[href^=mailto]');
-            return el.textContent.trim();
+            if (el) {
+              return el.textContent.trim();
+            }
+            else {
+              return 'no email address found in user page';
+            }
           });
+          console.warn('Wait 4s to ease load on server...');
+          await sleep(4000);
+          console.warn('Wait 4s to ease load on server... done');
         }
         finally {
           page.close();
         }
-        console.warn('Wait 1s to ease load on server...');
-        await sleep(1000);
-        console.warn('Wait 1s to ease load on server... done');
       }
     }
     finally {