Why aren't you using wxString everywhere anyway?
Well, we could use wxString for that,
file.Read(wxStringBuffer(buff, len+1), len); does just that... but it only adds a lot of overhead.
Rather than using a function that allocates buffers and reads data from disk, then makes a copy only to discard it a millisecond later, it would be better to use the FileManager for loading, anyway. This would make use of editors that are already loaded into memory, remove two allocations and memory copies, offer better I/O balancing, and be able to read from URLs.
But for the meantime, this is a nice catch, Rick.