Check for poptConfigLine() return code in poptReadConfigFile()
Check for poptConfigLine() return code in poptReadConfigFile()

As of now, poptConfigLine() always returns 0 so this is a essentially
a no-op, but preparing for those errors seems much more meaningful than
grabbing the return code into an unused variable which the compiler will
whine about. Move the free() after exit to ensure no memory leaks
if/when poptConfigLine() starts returning errors.

GerHobbelt/POPT,GerHobbelt/POPT,GerHobbelt/POPT