pseudoref: check return values from read_ref()

These codepaths attempt to compare the "expected" current value with
the actual current value, but did not check if we successfully read
the current value before comparison.

Signed-off-by: David Turner <dturner@twopensource.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: dturner-tw

refs.c

@@ -2868,7 +2868,9 @@ static int write_pseudoref(const char *pseudoref, const unsigned char *sha1,
 
 	if (old_sha1) {
 		unsigned char actual_old_sha1[20];
-		read_ref(pseudoref, actual_old_sha1);
+
+		if (read_ref(pseudoref, actual_old_sha1))
+			die("could not read ref '%s'", pseudoref);
 		if (hashcmp(actual_old_sha1, old_sha1)) {
 			strbuf_addf(err, "Unexpected sha1 when writing %s", pseudoref);
 			rollback_lock_file(&lock);
@@ -2904,7 +2906,8 @@ static int delete_pseudoref(const char *pseudoref, const unsigned char *old_sha1
 					       LOCK_DIE_ON_ERROR);
 		if (fd < 0)
 			die_errno(_("Could not open '%s' for writing"), filename);
-		read_ref(pseudoref, actual_old_sha1);
+		if (read_ref(pseudoref, actual_old_sha1))
+			die("could not read ref '%s'", pseudoref);
 		if (hashcmp(actual_old_sha1, old_sha1)) {
 			warning("Unexpected sha1 when deleting %s", pseudoref);
 			rollback_lock_file(&lock);