Keep attachment files for a while

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

@@ -147,7 +147,8 @@ public class WorkerCleanup extends Worker {
             Log.i("Cleanup attachment files");
             File[] attachments = new File(context.getFilesDir(), "attachments").listFiles();
             if (attachments != null)
-                for (File file : attachments) {
+                for (File file : attachments)
+                    if (manual || file.lastModified() + KEEP_FILES_DURATION < now) {
                         long id = Long.parseLong(file.getName().split("\\.")[0]);
                         EntityAttachment attachment = db.attachment().getAttachment(id);
                         if (attachment == null || !attachment.available) {