Add a missing PROC_UNLOCK in ptrace() for the PT_IO case.
Add a missing PROC_UNLOCK in ptrace() for the PT_IO case.

PR:		kern/44065
Submitted by:	Mark Kettenis <kettenis@chello.nl>

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase