thread out_listener and err_listener don't stop when subprocess finished.

[SailFlorve]

Sample code is:

_subpiper = _SubPiper(
    "ls"
)
_subpiper.execute()
print("")

when I put a breakpoint on print statement, the _SubPiper object should totally be deleted. But in Resource Monitor, I can see the CPU keeps 30% usage and memory usage keeps increasing.

[waszil]

You're right, I've fixed this.