suppressed fopen warning

When trying to write to a file that does not exist i.e `test/test.csv` `fopen` outputs the warning: 

```
PHP Warning:  fopen(test/test.csv): failed to open stream: No such file or directory in...
```

This is correct, but with you throwing an exception immediately after the `fopen` (if there is no file pointer) then i think it is safe to suppress this error (as you are handling it with the exception anyway).