format_trailer_info(): move "fast path" to caller

This is another preparatory refactor to unify the trailer formatters.

This allows us to drop the "msg" parameter from format_trailer_info(),
so that it take 3 parameters, similar to format_trailers() which also
takes 3 parameters:

    void format_trailers(const struct process_trailer_options *opts,
                         struct list_head *trailers,
                         struct strbuf *out)

The short-term goal is to make format_trailer_info() be smart enough to
deprecate format_trailers(). And then ultimately we will rename
format_trailer_info() to format_trailers().

Signed-off-by: Linus Arver <linusa@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

trailer.c

@@ -1087,21 +1087,11 @@ void trailer_info_release(struct trailer_info *info)
 
 static void format_trailer_info(const struct process_trailer_options *opts,
 				const struct trailer_info *info,
-				const char *msg,
 				struct strbuf *out)
 {
 	size_t origlen = out->len;
 	size_t i;
 
-	/* If we want the whole block untouched, we can take the fast path. */
-	if (!opts->only_trailers && !opts->unfold && !opts->filter &&
-	    !opts->separator && !opts->key_only && !opts->value_only &&
-	    !opts->key_value_separator) {
-		strbuf_add(out, msg + info->trailer_block_start,
-			   info->trailer_block_end - info->trailer_block_start);
-		return;
-	}
-
 	for (i = 0; i < info->trailer_nr; i++) {
 		char *trailer = info->trailers[i];
 		ssize_t separator_pos = find_separator(trailer, separators);
@@ -1153,7 +1143,15 @@ void format_trailers_from_commit(const struct process_trailer_options *opts,
 	struct trailer_info info;
 
 	trailer_info_get(opts, msg, &info);
-	format_trailer_info(opts, &info, msg, out);
+	/* If we want the whole block untouched, we can take the fast path. */
+	if (!opts->only_trailers && !opts->unfold && !opts->filter &&
+	    !opts->separator && !opts->key_only && !opts->value_only &&
+	    !opts->key_value_separator) {
+		strbuf_add(out, msg + info.trailer_block_start,
+			   info.trailer_block_end - info.trailer_block_start);
+	} else
+		format_trailer_info(opts, &info, out);
+
 	trailer_info_release(&info);
 }