wc: stop processing --files0-from input after stdout write failure

[mattsu2020]

Summary

Fix wc --files0-from=- so it stops processing additional inputs after a stdout write failure.

With an unbounded --files0-from stream (e.g. yes /dev/null | tr '\n' '\0') and a failing stdout write, wc kept iterating and repeatedly printed:

wc: failed to print result for /dev/null: No space left on device

This could lead to the process not exiting as expected.

Fixes #11009.

Root cause

In the per-input loop, print_stats(...) errors were reported but not treated as a terminal condition.
As a result, wc continued consuming more paths from --files0-from=- even after stdout was no longer writable.

Changes

• src/uu/wc/src/wc.rs

  • After reporting wc-error-failed-to-print-result, return from wc(...) immediately.
  • This prevents repeated write-error spam and allows the process to terminate.

• tests/by-util/test_wc.rs

  • Add Linux-only regression test:
    • test_files0_stops_after_stdout_write_error
  • The test writes stdout to /dev/full and verifies that:
    • failed to print result for /dev/null is emitted only once.

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/tty/tty-eof (passes in this run but fails in the 'main' branch)
Note: The gnu test tests/basenc/bounded-memory is now being skipped but was previously passing.
Note: The gnu test tests/expand/bounded-memory is now being skipped but was previously passing.

[cakebaker]

Thanks!