There are several ways of removing this limitation:
do what you currently do manually in load(AssetInfo) before creating the scanner, it would increase a lot the memory footprint whereas there are tons of obj files without backslash
override the scanner so that it treats several consecutive lines ended with a backslash and the next one as a single line, it wouldn’t increase the memory footprint and it would avoid invasive changes in the current code
don’t use a scanner, use a BufferedReader, treat the backslash very early like here
My third suggestion is the easiest and most efficient one. I suggest you to write a patch and to provide an example of obj file. Good luck.