Bug 1865154 - Add check for activeIndex in tabState.entries r=sessionstore-reviewers,sfoster

* Only add previously open tabs to the newWindowState in _prepDataForDeferredRestore
if they have entries

Differential Revision: https://phabricator.services.mozilla.com/D196157

browser/components/sessionstore/SessionStore.sys.mjs

@@ -6532,6 +6532,7 @@ var SessionStoreInternal = {
           activeIndex = Math.min(activeIndex, tabState.entries.length - 1);
           activeIndex = Math.max(activeIndex, 0);
 
+          if (activeIndex in tabState.entries) {
             let title =
               tabState.entries[activeIndex].title ||
               tabState.entries[activeIndex].url;
@@ -6555,6 +6556,7 @@ var SessionStoreInternal = {
               );
             }
           }
+        }
         tIndex++;
       }