<rdar://problem/12831670>

When using the same-device optimization for shared cache libraries, if
we have an invalid load address for __LINKEDIT, don't try to read
anything out of lldb's own address space.  Reading it out of the remote
address space will fail gracefully if we have bad addresses but reading
it out of lldb's own address space will result in a crash.

llvm-svn: 169582