cmp: fix bug in -b diagnostic

Problem reported by mancha (Bug#32249).
* src/cmp.c (count_newlines): Restore old value of sentinel.
* tests/cmp: Test for the bug.

1 files changed, 10 insertions, 0 deletions

diff --git a/tests/cmp b/tests/cmp
index 160c1ea..ca0fe5e 100755
--- a/tests/cmp
+++ b/tests/cmp
@@ -208,4 +208,14 @@ done >out1
 
 compare exp1 out1 || fail=1
 
+printf 'bad\n' >bad
+printf 'bug\n' >bug
+echo LC_ALL=C cmp -b bad bug
+LC_ALL=C cmp -b bad bug
+test $? -eq 1 || fail=1
+case `LC_ALL=C cmp -b bad bug` in
+  'bad bug differ: byte 2, line 1 is '*' a '*' u') ;;
+  *) echo 'expected cmp -b to report a and u'; fail=1;;
+esac
+
 Exit $fail