Patch from Todd Fiala: lldb will seg fault if for some reason there is no unwinder when StackFrameList::GetFramesUpTo() is called.

Mainly patched to stop LLDB from crashing. This can easily happen if you debug to a remote gdbserver that doesn't have any dynamic register info and you don't have a target definition file specified.



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@195499 91177308-0d34-0410-b5e6-96231b3b80d8