Exception when parsing empty file

[SamK]

# python --version
Python 2.7.3
# touch tempfile
# ./check_iftraffic_nrpe.py -f tempfile
Traceback (most recent call last):
  File "./check_iftraffic_nrpe.py", line 627, in <module>
    main(default_values)
  File "./check_iftraffic_nrpe.py", line 497, in main
    uptime0, procnetdev0 = datafile.read()
  File "./check_iftraffic_nrpe.py", line 125, in read
    self.uptime = float(content[0])
IndexError: list index out of range