This fixes a SIGSEGV failure in ReaderArchive while trying to trace what
InputFile is being pulled from the Archive library to resolve a symbol. 

The buffer which was being used was already being handed over to the
MemoryBuffer object and was being accessed after the hand over. 

Moving it before the buffer is handed over.


git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@178838 91177308-0d34-0410-b5e6-96231b3b80d8