Check if theres's a target before trying to actually poke at it

Works around a bug in LLDB from Xcode5+ where it either:

* Tries to call the stop hook before the inferior has properly started
OR
* Returns garbage when you ask for the inferiors registers due to some
  sweet race condition.

Either way, test first, and mock em out for gdb that evidently does the
right thing
Merge pull request #20 from richo/master

Check if theres's a target before trying to actually poke at it