[llvm-objdump] Don't disassemble symbols before SectionAddr

This was caught by UBSAN

tools/llvm-objdump/X86/macho-disassembly-g-dsym.test
tools/llvm-objdump/X86/hex-displacement.test

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@358806 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed