finfo_open returns false instead of null on failure

[dbrekelmans]

In Safe\finfo_open we throw an exception when \finfo_open returns null. But occording to the docs, the function returns false on failure instead of null. So we should be throwing an exception when \finfo_open returns false.

Returns a magic database resource on success or false on failure.

https://www.php.net/manual/en/function.finfo-open

[Duroth]

@dbrekelmans No longer reproducable, it seems.