Workaround wrong attachment content types

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

@@ -1224,9 +1224,9 @@ public class MessageHelper {
                     // For example, sometimes PDF files are sent as application/octet-stream
                     if (!apart.pgp) {
                         String extension = Helper.getExtension(apart.attachment.name);
-                        if (extension != null &&
-                                ("pdf".equals(extension.toLowerCase(Locale.ROOT)) ||
-                                        "application/octet-stream".equals(apart.attachment.type))) {
+                        if (extension != null) {
+                            if ("application/zip".equals(apart.attachment.type) ||
+                                    "application/octet-stream".equals(apart.attachment.type)) {
                                 String type = MimeTypeMap.getSingleton()
                                         .getMimeTypeFromExtension(extension.toLowerCase(Locale.ROOT));
                                 if (type != null) {
@@ -1236,6 +1236,7 @@ public class MessageHelper {
                                 }
                             }
                         }
+                    }
 
                     if (apart.attachment.size <= 0)
                         apart.attachment.size = null;