Grep currently special-cased empty pattern file to be the same as
pattern file with one empty line (empty pattern). That does mirror how
GNU grep behaves, except when -x is provided. In that case .* pattern
needs to be used instead.
Signed-off-by: Gray Wolf <wolf@wolfsden.cz>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>