BundleFile: fix exception on file.save("original") - #178

On a slightly related note (I’d open a separate GitHub issue, but it isn’t exactly a bug), save_fs should maybe throw if the data_flags argument includes the encryption flag, because (as far as I can tell) UnityPy doesn’t implement encryption upon saving. But this isn’t entirely trivial to implement because the argument may be passed as a raw integer, so you’d need to duplicate the version-dependent logic from read_fs just to figure out what the integer means.

Thanks for noticing and fixing the issue.
And you're right, it should error in case it's supposed to store an encrypted bundle.