Don't allow BIO_READ, BIO_WRITE or BIO_DELETE requests that are
fully beyond the end of providers media. The only exception is made
for the zero length transfers which are allowed to be just on the
boundary. Previously, any requests starting on the boundary (i.e. next
byte after the last one) have been allowed to go through.

No response from: freebsd-geom@, phk
MFC after: 1 month