tail: fix -c +N. Closes 4111

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/testsuite/tail.tests b/testsuite/tail.tests
index 7140da2..305a83b 100755
--- a/testsuite/tail.tests
+++ b/testsuite/tail.tests
@@ -14,4 +14,12 @@
 	"0\n" \
 	"" "qw"
 
+testing "tail: -c +N with largish N" \
+	"
+	dd if=/dev/zero bs=16k count=1 2>/dev/null | tail -c +8200 | wc -c;
+	dd if=/dev/zero bs=16k count=1 2>/dev/null | tail -c +8208 | wc -c;
+	" \
+	"8185\n8177\n" \
+	"" ""
+
 exit $FAILCOUNT