Division by zero

Details:
https://nvd.nist.gov/vuln/detail/CVE-2019-14249

Fix:
https://sourceforge.net/p/libdwarf/code/ci/cb7198abde46c2ae29957ad460da6886eaa606ba/tree/libdwarf/dwarf_elf_load_headers.c?diff=99e77c3894877a1dd80b82808d8309eded4e5599