builtin/am: make sure state files are text

We forgot to terminate the payload given to write_file() with LF,
resulting in files that end with an incomplete line.  Teach the
wrappers builtin/am uses to make sure it adds LF at the end as
necessary.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/am.c

@@ -199,13 +199,19 @@ static inline const char *am_path(const struct am_state *state, const char *path
 static int write_state_text(const struct am_state *state,
 			    const char *name, const char *string)
 {
-	return write_file(am_path(state, name), 1, "%s", string);
+	const char *fmt;
+
+	if (*string && string[strlen(string) - 1] != '\n')
+		fmt = "%s\n";
+	else
+		fmt = "%s";
+	return write_file(am_path(state, name), 1, fmt, string);
 }
 
 static int write_state_count(const struct am_state *state,
 			     const char *name, int value)
 {
-	return write_file(am_path(state, name), 1, "%d", value);
+	return write_file(am_path(state, name), 1, "%d\n", value);
 }
 
 static int write_state_bool(const struct am_state *state,