The entry size of the probe section is assumed to be at least
sizeof(dof_probe_t) by the loop further below.

enoff_sec->dofs_entsize was not being validated at all.

When multiplying an index by a table entry size, make sure the
multiplication can't overflow.

Fix an off-by-one when validating the translated probe argument array.

Make sure that the probe argument argvs are valid string offsets
even if the argument count is zero.