Fix LLDB RSP client to decode '$O' packets incorrectly

Character with ASCII code 0 is incorrectly treated by LLDB as the end of
RSP packet. The left of the debugger server output is silently ignored.

Patch from evgeny.leviant@gmail.com
Reviewed by: clayborg
Subscribers: lldb-commits
Differential Revision: http://reviews.llvm.org/D12523

llvm-svn: 247908