fixed 6ee8e141 from https://gitee.com/arvinzzz/third_party_musl/pulls/177

fix: 修复fopen入参检验不全导致访问异常

当mode入参为空也做错误返回

close: #I4N0WY
Signed-off-by: Narvinzzz <zhaotianyu9@huawei.com>
Change-Id: I0b0b997b6498b53da6324ea60d2502c3d2e80be3

porting/liteos_m/kernel/src/stdio/fopen.c

@@ -12,7 +12,7 @@ FILE *fopen(const char *restrict filename, const char *restrict mode)
 	int flags;
 
 	/* Check for valid initial mode character */
-	if (!strchr("rwa", *mode)) {
+	if ((mode == NULL) || (!strchr("rwa", *mode))) {
 		errno = EINVAL;
 		return 0;
 	}