fread错误使用

[DongwenHuang]

int ret = fread(data, size, 1, file_);
if (size == 0 || ret == 0) return false;
if (ret == -1) {}

上面是你的filesystem.cc的代码，这段代码有错误，fread不会返回-1，当返回0的时候应该用feof,ferror来检测是什么原因导致返回的数目比1少，发生错误到关闭

引用下面这段话：
RETURN VALUE
fread and fwrite return the number of items successfully read or written (i.e., not the number of
characters). If an error occurs, or the end-of-file is reached, the return value is a short item
count (or zero).

   fread does not distinguish between end-of-file and error, and callers must use feof(3) and ferror(3)
   to determine which occurred.

[liyichao]

Thanks, can you create a pull request ?