Fix ls failing when end of string falls on 512 boundary

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My device wasn't working with QFile2Snes, nor a GRPC replacement I started writing after blaming QFile2Snes for being jank. Turns out it's a bug with SNI. When I request files for my device, the first returned packet looks like this -

01616c74747072202d204e6f476c6974636865732d6f70656e2d67616e6f6e5f34417670644b7a34766e2e7366630001616c74747072202d204e6f476c697463 
6865732d6f70656e2d67616e6f6e5f4f6247626450654476502e7366630001616c74747072202d204e6f476c6974636865732d6f70656e2d67616e6f6e5f6f4c
7956376b365947622e736663000150325f7a69675f47306a7a716d6c3854372d4c5a722d7a664d496649412e7366630001616c74747072202d204e6f476c6974
636865732d6f70656e2d67616e6f6e5f67564d5237716e6f76352e7366630001616c74747072202d204e6f476c6974636865732d6f70656e2d67616e6f6e5f5a
654d34346130614d6a202831292e73666300014c5454504861636b2d7631332e312e312d656d756c61746f722d637573746f6d6875642e7366630001424d5f4d 
37393838333831313939373932303334343138365f50325f7a69672e7366630001424d5f3639343230313333375f50325f5a69675f6e6f6c6f6769635f6e6f72
6d616c2d6e6f726d616c2d6f70656e2d67616e6f6e5f76616e696c6c612d62616c616e6365642e7366630001424d5f3639343230313333375f50325f5a69675f
6e6f6c6f6769635f6e6f726d616c2d6e6f726d616c2d6f70656e2d67616e6f6e5f76616e696c6c612d62616c616e6365642d6b657973616e6974792e73666300    

• it looks like reading a 0x02 for "there's more data here" is just an optimization and you really really need to just keep reading as long as you don't get 0xFF. This patch appears to fix things for me locally.