Fix the ability of "lldb-platform" to upload files.

The issue was GDBRemoteCommunication::CheckForPacket() already fixes up any prefixed bytes (0x7d followed by value that is XOR'ed with 0x20). If we do this again, we cause binary packets to lose bytes.

This allows lldb-platform to be able to upload binaries and debug them remotely.

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@218002 91177308-0d34-0410-b5e6-96231b3b80d8