zgrep: fix exit status with multiple files

[vangyzen]

Summary

zgrep should exit with success when given multiple files and the
pattern is found in at least one file. Prior to this change,
it would exit with success only if the pattern was found in _every_ file.

Test Plan

The added test case failed before the fix. All tests pass with the fix.

grep_test:zgrep_multiple_files  ->  passed  [0.022s]

Results file id is usr_tests_usr.bin_grep.20200930-212653-629287
Results saved to /root/.kyua/store/results.usr_tests_usr.bin_grep.20200930-212653-629287.db

52/52 passed (0 failed)

[ngie]

contrib/netbsd-tests/usr.bin/grep/t_grep.sh

898 ↗

(On Diff #77704)

"Ensures that zgrep functions properly with multiple files" would be a better comment.

[vangyzen]

contrib/netbsd-tests/usr.bin/grep/t_grep.sh

898 ↗

(On Diff #77704)

Indeed, it would. (I'm guilty of copy-and-paste.)