pickaxe -S: support content with NULs under --pickaxe-regex

Fix a bug in the matching routine powering -S<rx> --pickaxe-regex so
that we won't abort early on content that has NULs in it.

We've had a hard requirement on REG_STARTEND since 2f8952250a (regex:
add regexec_buf() that can work on a non NUL-terminated string,
2016-09-21), but this sanity check dates back to d01d8c6782 (Support
for pickaxe matching regular expressions, 2006-03-29).

It wasn't needed anymore, and as the now-passing test shows, actively
getting in our way. Since we always require REG_STARTEND support we do
not need to stop at NULs. If we are dealing with a haystack with NUL
in it. The needle may be behind that NUL.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diffcore-pickaxe.c

@@ -78,12 +78,12 @@ static unsigned int contains(mmfile_t *mf, regex_t *regexp, kwset_t kws)
 		regmatch_t regmatch;
 		int flags = 0;
 
-		while (sz && *data &&
+		while (sz &&
 		       !regexec_buf(regexp, data, sz, 1, &regmatch, flags)) {
 			flags |= REG_NOTBOL;
 			data += regmatch.rm_eo;
 			sz -= regmatch.rm_eo;
-			if (sz && *data && regmatch.rm_so == regmatch.rm_eo) {
+			if (sz && regmatch.rm_so == regmatch.rm_eo) {
 				data++;
 				sz--;
 			}

t/t4209-log-pickaxe.sh

@@ -215,4 +215,12 @@ test_expect_success 'log -S looks into binary files' '
 	test_cmp log full-log
 '
 
+test_expect_success 'log -S --pickaxe-regex looks into binary files' '
+	git -C GS-bin-txt log --pickaxe-regex -Sa >log &&
+	test_cmp log full-log &&
+
+	git -C GS-bin-txt log --pickaxe-regex -S"[a]" >log &&
+	test_cmp log full-log
+'
+
 test_done