Crash in dataFromBase64String

[benweiss]

If the input string contains no valid base64 data, this routine will crash. For instance: if the input is a string containing just spaces (and thus no valid base64 data), then NewBase64Decode() returns a valid pointer but an invalid (-1) length. dataFromBase64String() subsequently tries to allocate a NSData block of size (-1), which crashes. This situation should be checked for and handled appropriately.