AddressSpace: fix DWARF based unwinding handling on Android

It is possible that there are no program headers in the module.  Do not
attempt to dereference nullptr as a program header.

git-svn-id: https://llvm.org/svn/llvm-project/libunwind/trunk@299591 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed