Error on default case in EXIF LatLng method

[blixenkrone]

Hello!

In the

switch tag.Format() {
	case tiff.RatVal:

the set tag.format struct value doesn't seem to be correct. (exif.go L: 482).
My images, which contains valid EXIF data, is not being seen as RatVal or StringVal, so the default case catches it, and returns an error. If i insert the logic from the tiff.RatVal case, the output of LatLng is correct.
I'm not one to make suggestions, but i'm guessing there's a minor bug here.

I can provide code/pictures if needed.

Thank you for a good lib!