get_parent_pid: fix memory leak
get_parent_pid: fix memory leak

Found through static analysis.

ascent12/sway,ascent12/sway,SirCmpwn/sway,1ace/sway,taiyu-len/sway,1ace/sway,1ace/sway,taiyu-len/sway,taiyu-len/sway,ascent12/sway