bug#20088: -a changes whether a match is found

[Jim Meyering]

--text (-a) is documented to change only the output, not grep's exit status.
Yet, it does change the exit status here:

  $ printf "a\0b\n" | LC_ALL=C src/grep -la a.b; echo $?
  (standard input)
  0
  $ printf "a\0b\n" | LC_ALL=C src/grep -l  a.b; echo $?
  1

Noted by Andreas Schwab in https://bugs.gnu.org/20080.