Fix NPE bug and clean up logic for setting the title bar

Author: niftynei

app/src/main/java/com/zulip/android/activities/ZulipActivity.java

@@ -460,27 +460,24 @@ public void onListResume(MessageListFragment list) {
         currentList = list;
 
         NarrowFilter filter = list.filter;
-
         if (filter == null) {
-            if (android.os.Build.VERSION.SDK_INT >= 11) {
-                getActionBar().setTitle("Zulip");
-                getActionBar().setSubtitle(null);
-            }
+            setupTitleBar(getString(R.string.app_name), null);
             this.drawerToggle.setDrawerIndicatorEnabled(true);
         } else {
-            String title = list.filter.getTitle();
-            if (android.os.Build.VERSION.SDK_INT >= 11) {
-                if (title != null) {
-                    getActionBar().setTitle(title);
-                }
-                getActionBar().setSubtitle(list.filter.getSubtitle());
-            }
+            setupTitleBar(filter.getTitle(), filter.getSubtitle());
             this.drawerToggle.setDrawerIndicatorEnabled(false);
         }
 
         this.drawerLayout.closeDrawers();
     }
 
+    private void setupTitleBar(String title, String subtitle) {
+        if (android.os.Build.VERSION.SDK_INT >= 11 && getActionBar() != null) {
+            if (title != null) getActionBar().setTitle(title);
+            getActionBar().setSubtitle(subtitle);
+        }
+    }
+
     public void doNarrow(NarrowFilter filter) {
         narrowedList = MessageListFragment.newInstance(filter);
         // Push to the back stack if we are not already narrowed