`grep` - with `-m 0` still opens files instead of short-circuiting like GNU (errors on a missing file GNU never touches)

[sylvestre]

GNU grep treats -m 0 / --max-count=0 as "stop before reading any line": it
never opens the input file at all, so a nonexistent file produces no error and
the run exits 1 (no match). uu_grep opens the file first and only then
applies the max-count, so a missing file yields a No such file or directory
error and exit 2.

Rust (incorrect - errors on the missing file)

$ ./target/release/grep -e x -m 0 /no/such/file
grep: /no/such/file: No such file or directory (os error 2)
# Exit code: 2

GNU (correct - short-circuits, never opens the file)

$ LC_ALL=C /usr/bin/grep -e x -m 0 /no/such/file
# (no output)
# Exit code: 1

Scope

• The divergence is specific to -m 0. With -m 1 on the same missing file
  both implementations error and exit 2.
• On an existing file, -m 0 already behaves correctly in both (no output,
  exit 1) — only the file-opening side effect differs.