Fix bug in IOSChromeSyncedTabDelegate::GetSessionStorageIfNeeded

Bug: 1033180, 1024750
Change-Id: I55719298534c29e6a5387c37671363fb0a3ce493
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1975611Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Commit-Queue: Olivier Robin <olivierrobin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#726316}

ios/chrome/browser/sync/ios_chrome_synced_tab_delegate.mm

@@ -224,8 +224,10 @@ bool IOSChromeSyncedTabDelegate::GetSessionStorageIfNeeded() const {
   bool should_use_storage =
       web_state_->GetNavigationManager()->IsRestoreSessionInProgress();
   bool storage_has_tabs = false;
-  if (should_use_storage && !session_storage_) {
-    session_storage_ = web_state_->BuildSessionStorage();
+  if (should_use_storage) {
+    if (!session_storage_) {
+      session_storage_ = web_state_->BuildSessionStorage();
+    }
     storage_has_tabs = session_storage_.itemStorages.count;
 #if DCHECK_IS_ON()
     if (storage_has_tabs) {