Add throwing error when unable to open file on iOS

[markholland]

We are migrating from rn-fetch-blob openDocument to this library for opening files from our app.

With this library, on Android if a file can't be opened an error is thrown but this isn't the case on iOS.

With rn-fetch-blob we did have this behaviour on iOS and would like to keep it.

Is there a reason why failing to open a file on iOS isn't considered as an error?

Here is the relevant code in rn-fetch-blob https://github.com/joltup/rn-fetch-blob/blob/master/ios/RNFetchBlob/RNFetchBlob.m#L610

Thanks in advance