Prevent crash

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

@@ -240,6 +240,8 @@ public class HtmlHelper {
 
     static String getQuote(Context context, long id, boolean sanitize) throws IOException {
         EntityMessage message = DB.getInstance(context).message().getMessage(id);
+        if (message == null)
+            return null;
         String html = EntityMessage.read(context, id);
         return String.format("<p>%s %s:</p>\n<blockquote>%s</blockquote>",
                 Html.escapeHtml(new Date(message.received).toString()),