Add null check for PageInfo storage fetch

mSubpage can be null if a storage fetch finishes after the
subpage has been left.

Bug: 1156888
Change-Id: Ib24378750a87606d36032f338486499ef7725819
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2589873Reviewed-by: Ehimare Okoyomon <eokoyomon@chromium.org>
Commit-Queue: Christian Dullweber <dullweber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836633}

components/page_info/android/java/src/org/chromium/components/page_info/PageInfoCookiesController.java

@@ -101,7 +101,9 @@ public class PageInfoCookiesController
 
         mWebsite = SingleWebsiteSettings.mergePermissionAndStorageInfoForTopLevelOrigin(
                 address, result);
-        mSubPage.setStorageUsage(mWebsite.getTotalUsage());
+        if (mSubPage != null) {
+            mSubPage.setStorageUsage(mWebsite.getTotalUsage());
+        }
     }
 
     private void onCheckedChangedCallback(boolean state) {