Show date header on sorting on unread, flagged or priority

app/src/main/java/eu/faircode/email/FragmentMessages.java

@@ -330,6 +330,13 @@ public class FragmentMessages extends FragmentBase implements SharedPreferences.
     private static final long REVIEW_ASK_DELAY = 21 * 24 * 3600 * 1000L; // milliseconds
     private static final long REVIEW_LATER_DELAY = 3 * 24 * 3600 * 1000L; // milliseconds
 
+    private static final List<String> SORT_DATE_HEADER = Collections.unmodifiableList(Arrays.asList(
+            "time",
+            "unread",
+            "starred",
+            "priority"
+    ));
+
     private static final List<String> DUPLICATE_ORDER = Collections.unmodifiableList(Arrays.asList(
             EntityFolder.INBOX,
             EntityFolder.OUTBOX,
@@ -607,7 +614,7 @@ public class FragmentMessages extends FragmentBase implements SharedPreferences.
             }
 
             private View getView(View view, RecyclerView parent, int pos) {
-                if (!date || !"time".equals(adapter.getSort()))
+                if (!date || !SORT_DATE_HEADER.contains(adapter.getSort()))
                     return null;
 
                 if (pos == NO_POSITION)