Check multiparts

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

@@ -2372,7 +2372,9 @@ public class MessageHelper {
                 if ("application/pgp-signature".equals(protocol) ||
                         "application/pkcs7-signature".equals(protocol) ||
                         "application/x-pkcs7-signature".equals(protocol)) {
-                    Multipart multipart = (Multipart) part.getContent();
+                    Object content = part.getContent();
+                    if (content instanceof Multipart) {
+                        Multipart multipart = (Multipart) content;
                         if (multipart.getCount() == 2) {
                             getMessageParts(multipart.getBodyPart(0), parts, null);
                             getMessageParts(multipart.getBodyPart(1), parts,
@@ -2405,13 +2407,17 @@ public class MessageHelper {
                                 sb.append(' ').append(i).append('=').append(multipart.getBodyPart(i).getContentType());
                             Log.e(sb.toString());
                         }
+                    } else
+                        throw new MessagingException("Multipart=" + (content == null ? null : content.getClass().getName()));
                 } else
                     Log.e(ct.toString());
             } else if (part.isMimeType("multipart/encrypted")) {
                 ContentType ct = new ContentType(part.getContentType());
                 String protocol = ct.getParameter("protocol");
                 if ("application/pgp-encrypted".equals(protocol) || protocol == null) {
-                    Multipart multipart = (Multipart) part.getContent();
+                    Object content = part.getContent();
+                    if (content instanceof Multipart) {
+                        Multipart multipart = (Multipart) content;
                         if (multipart.getCount() == 2) {
                             // Ignore header
                             getMessageParts(multipart.getBodyPart(1), parts, EntityAttachment.PGP_MESSAGE);
@@ -2423,6 +2429,8 @@ public class MessageHelper {
                                 sb.append(' ').append(i).append('=').append(multipart.getBodyPart(i).getContentType());
                             Log.e(sb.toString());
                         }
+                    } else
+                        throw new MessagingException("Multipart=" + (content == null ? null : content.getClass().getName()));
                 } else
                     Log.e(ct.toString());
             } else if (part.isMimeType("application/pkcs7-mime") ||