Fixing sd_imageOrientationFromImageData call crashes if image is nil, re...

We have seen that SDWebImage has added support for image orientation that our apps are crashing now on line 63 of UIImage+MultiFormat.m.

I do not know why, but on some circumstances it might be that imageData is nil. If that is the case, imageSource would be imageSource pointing to 0x00000000, and CFRelease'ing it throws an exception that crashes the whole app.

My suggested fix, since this method is used only once, would be to check for nil on sd_imageWithData.