Improved error message

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

@@ -2002,6 +2002,9 @@ public class MessageHelper {
                 try {
                     contentType = new ContentType(part.getContentType());
                 } catch (ParseException ex) {
+                    if (part instanceof MimeMessage)
+                        Log.e("MimeMessage content type=" + ex.getMessage());
+                    else
                         Log.w(ex);
                     contentType = new ContentType(Helper.guessMimeType(filename));
                 }