Prevent double release of mach ports

Summary:
When a MIG routine returns KERN_FAILURE, the demux function will release any OOL resources like ports. In this case, task_port and thread_port will be released twice, potentially resulting in use after free of the ports.

I don't think we can test this in any useful way
rdar://problem/37331387

Reviewers: jasonmolenda

Subscribers: lldb-commits

Differential Revision: https://reviews.llvm.org/D45011

llvm-svn: 328761