nlist: Check that e_shnum and e_shentsize are within bounds

nlist: Check that e_shnum and e_shentsize are within bounds

The e_shnum must not be 0, otherwise we will do a zero sized allocation
and further processing of the executable will lead to out of bounds
read/write accesses. The e_shentsize must be equal to sizeof(Elf_Shdr),
otherwise we will perform out of bounds read accesses on the shdr array.

Reported-by: Daniel Hodson <daniel@elttam.com.au>
Based-on-patch-by: Daniel Hodson <daniel@elttam.com.au>
Signed-off-by: Guillem Jover <guillem@hadrons.org>