[LOW] STR #4052: 'lp(r) < /dev/null' return successful-ok

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[STR New]

Reporting as suggested in STR #4015.

The fix from STR #4015 causes a regression in a sense that
'lpr < /dev/null' and 'lp < /dev/null'
return successful-ok while previously the return string was
'No file in print request.'

Link: http://www.cups.org/str.php?L4052
Version: 1.6-current