Account for missing NSFileProtectionKey file attribute key.

Ok, after doing a bit of testing, it appears that the NSFileProtectedKey is not included in the file attributes dictionary while running on the iOS simulator. It *does* get returned on a device, however. I tested on iOS 7.0.6.

Therefore, this patch will assume that we can reuse the existing log file if the NSFileProtectedKey is missing. If you're not comfortable with this, we could add checks for #if TARGET_IPHONE_SIMULATOR to fine-tune this condition.

Thanks!