[Object/ELF] - Do not crash if string table sh_size is equal to zero.

Revealed using "id_000038,sig_11,src_000015,op_havoc,rep_16" from PR30540,
when sh_size was 0, crash happened.

Differential revision: https://reviews.llvm.org/D25091

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@285282 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed