clear old pinned items stored in wrong position

fix #12941

app/sessionStore.js

@@ -847,6 +847,16 @@ module.exports.runPreMigrations = (data) => {
       if (data.cache) {
         delete data.cache.bookmarkLocation
       }
+
+      // pinned top sites were stored in the wrong position in 0.19.x
+      // allowing duplicated items. See #12941
+      // in this case eliminate pinned items so they can be properly
+      // populated in their own indexes
+      if (data.about.newtab.pinnedTopSites) {
+        // Empty array is currently set to include default pinned sites
+        // which we avoid given the user already have a profile
+        data.about.newtab.pinnedTopSites = [null]
+      }
     }
   }