use strbuf_complete_line() for adding a newline if needed

Call strbuf_complete_line() instead of open-coding it.  Also remove
surrounding comments indicating the intent to complete a line since
this information is already included in the function name.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/fmt-merge-msg.c

@@ -216,8 +216,7 @@ static void add_branch_desc(struct strbuf *out, const char *name)
 			strbuf_addf(out, "  : %.*s", (int)(ep - bp), bp);
 			bp = ep;
 		}
-		if (out->buf[out->len - 1] != '\n')
-			strbuf_addch(out, '\n');
+		strbuf_complete_line(out);
 	}
 	strbuf_release(&desc);
 }

notes-utils.c

@@ -44,8 +44,7 @@ void commit_notes(struct notes_tree *t, const char *msg)
 
 	/* Prepare commit message and reflog message */
 	strbuf_addstr(&buf, msg);
-	if (buf.buf[buf.len - 1] != '\n')
-		strbuf_addch(&buf, '\n'); /* Make sure msg ends with newline */
+	strbuf_complete_line(&buf);
 
 	create_notes_commit(t, NULL, buf.buf, buf.len, commit_sha1);
 	strbuf_insert(&buf, 0, "notes: ", 7); /* commit message starts at index 7 */

trace.c

@@ -122,9 +122,7 @@ static int prepare_trace_line(const char *file, int line,
 
 static void print_trace_line(struct trace_key *key, struct strbuf *buf)
 {
-	/* append newline if missing */
-	if (buf->len && buf->buf[buf->len - 1] != '\n')
-		strbuf_addch(buf, '\n');
+	strbuf_complete_line(buf);
 
 	write_or_whine_pipe(get_trace_fd(key), buf->buf, buf->len, err_msg);
 	strbuf_release(buf);