Use app name for app description if filter null

app/src/main/java/com/todoroo/astrid/activity/MainActivity.java

@@ -304,7 +304,8 @@ public class MainActivity extends InjectingAppCompatActivity
     ThemeColor filterColor = getFilterColor();
     filterColor.applyToStatusBar(drawerLayout);
     filterColor.applyToNavigationBar(this);
-    filterColor.applyTaskDescription(this, filter.listingTitle);
+    filterColor.applyTaskDescription(
+        this, filter == null ? getString(R.string.app_name) : filter.listingTitle);
     theme.withThemeColor(filterColor).applyToContext(this);
   }