Always guess attachment type

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

@@ -1117,16 +1117,15 @@ public class MessageHelper {
 
                     // Try to guess a better content type
                     // For example, sometimes PDF files are sent as application/octet-stream
-                    if ("application/octet-stream".equalsIgnoreCase(apart.attachment.type)) {
                     String extension = Helper.getExtension(apart.attachment.name);
                     if (extension != null) {
                         String type = MimeTypeMap.getSingleton().getMimeTypeFromExtension(extension.toLowerCase());
                         if (type != null) {
+                            if (!type.equals(apart.attachment.type))
                                 Log.w("Guessing file=" + apart.attachment.name + " type=" + type);
                             apart.attachment.type = type;
                         }
                     }
-                    }
 
                     if (apart.attachment.size <= 0)
                         apart.attachment.size = null;