Ignore invalid lines in /proc/*/status files

Ignore invalid lines in /proc/*/status files

One Ubuntu Linux kernel security fix introduced a blank line.
Some other Linux kernels may have invalid lines in the future.

See-also: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1772671
Fixes: https://bugs.launchpad.net/ubuntu/+source/iotop/+bug/1772856
Reported-by: Paul Jaros <jaros.paul@gmail.com>
Reported-in: <CAEh_nc0_DXTmfu16PxmVyrCi6QQeSrpnGGhtfNu60wJYfa_6Zw@mail.gmail.com>
Traceback (most recent call last):
  File "/usr/sbin/iotop", line 17, in <module>
    main()
  File "/usr/lib/python2.7/dist-packages/iotop/ui.py", line 620, in main
    main_loop()
  File "/usr/lib/python2.7/dist-packages/iotop/ui.py", line 610, in <lambda>
    main_loop = lambda: run_iotop(options)
  File "/usr/lib/python2.7/dist-packages/iotop/ui.py", line 508, in run_iotop
    return curses.wrapper(run_iotop_window, options)
  File "/usr/lib/python2.7/curses/wrapper.py", line 43, in wrapper
    return func(stdscr, *args, **kwds)
  File "/usr/lib/python2.7/dist-packages/iotop/ui.py", line 501, in run_iotop_window
    ui.run()
  File "/usr/lib/python2.7/dist-packages/iotop/ui.py", line 155, in run
    self.process_list.duration)
  File "/usr/lib/python2.7/dist-packages/iotop/ui.py", line 434, in refresh_display
    lines = self.get_data()
  File "/usr/lib/python2.7/dist-packages/iotop/ui.py", line 415, in get_data
    return list(map(format, processes))
  File "/usr/lib/python2.7/dist-packages/iotop/ui.py", line 388, in format
    cmdline = p.get_cmdline()
  File "/usr/lib/python2.7/dist-packages/iotop/data.py", line 292, in get_cmdline
    proc_status = parse_proc_pid_status(self.pid)
  File "/usr/lib/python2.7/dist-packages/iotop/data.py", line 196, in parse_proc_pid_status
    key, value = line.split(':\t', 1)
ValueError: need more than 1 value to unpack