<rdar://problem/13413693>

Fixed a crasher in the new DWARF in .o files line table linking function where "back()" could end up being called on an empty std::vector.



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@177082 91177308-0d34-0410-b5e6-96231b3b80d8