use get_cached_commit_buffer where appropriate

Some call sites check commit->buffer to see whether we have
a cached buffer, and if so, do some work with it. In the
long run we may want to switch these code paths to make
their decision on a different boolean flag (because checking
the cache may get a little more expensive in the future).
But for now, we can easily support them by converting the
calls to use get_cached_commit_buffer.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/rev-list.c

@@ -106,7 +106,7 @@ static void show_commit(struct commit *commit, void *data)
 	else
 		putchar('\n');
 
-	if (revs->verbose_header && commit->buffer) {
+	if (revs->verbose_header && get_cached_commit_buffer(commit)) {
 		struct strbuf buf = STRBUF_INIT;
 		struct pretty_print_context ctx = {0};
 		ctx.abbrev = revs->abbrev;

log-tree.c

@@ -588,7 +588,7 @@ void show_log(struct rev_info *opt)
 		show_mergetag(opt, commit);
 	}
 
-	if (!commit->buffer)
+	if (!get_cached_commit_buffer(commit))
 		return;
 
 	if (opt->show_notes) {

object.c

@@ -197,7 +197,7 @@ struct object *parse_object_buffer(const unsigned char *sha1, enum object_type t
 		if (commit) {
 			if (parse_commit_buffer(commit, buffer, size))
 				return NULL;
-			if (!commit->buffer) {
+			if (!get_cached_commit_buffer(commit)) {
 				set_commit_buffer(commit, buffer);
 				*eaten_p = 1;
 			}