udf: Reject read requests with an invalid length

• If the size is negative or if rounding it up to a multiple of the block size overflows, fail the read request with ERANGE.

• While here, add a sanity check that the ICB length for the root directory is at least as long as a minimum-sized file entry.

PR: 257768
Reported by: Robert Morris <rtm@lcs.mit.edu>
MFC after: 1 week
Sponsored by: FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D41220