Win32: Try to fix handle leaks in capture_sync.

Win32: Try to fix handle leaks in capture_sync.

If CreateProcess succeeds, close our child's primary thread handle. As
the PROCESS_INFORMATION page at
https://msdn.microsoft.com/en-us/library/windows/desktop/ms684873.aspx
says,

    If the function succeeds, be sure to call the CloseHandle function
    to close the hProcess and hThread handles when you are finished with
    them. Otherwise, when the child process exits, the system cannot
    clean up the process structures for the child process because the
    parent process still has open handles to the child process.

Closing the handle immediately doesn't seem to do any harm here, but
add a note that we might want to store it and close it later.

In sync_interface_stats_open, close our message and data descriptors
after calling sync_pipe_wait_for_child.

Ping-Bug: 11702
Change-Id: I56e0625fdceb66fba822c2dc83e07d40844329a7
Reviewed-on: https://code.wireshark.org/review/11882
Petri-Dish: Gerald Combs <gerald@wireshark.org>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Gerald Combs <gerald@wireshark.org>
Reviewed-by: Anders Broman <a.broman58@gmail.com>