pstore: Avoid writing records with zero size

Sometimes pstore_console_write() will write records with zero size
to persistent ram zone, which is unnecessary. It will only increase
resource consumption. Also adjust ramoops_write_kmsg_hdr() to have
same logic if memory allocation fails.

Signed-off-by: Yue Hu <huyue2@yulong.com>
Signed-off-by: Kees Cook <keescook@chromium.org>

fs/pstore/platform.c

@@ -501,6 +501,9 @@ static void pstore_console_write(struct console *con, const char *s, unsigned c)
 {
 	struct pstore_record record;
 
+	if (!c)
+		return;
+
 	pstore_record_init(&record, psinfo);
 	record.type = PSTORE_TYPE_CONSOLE;