Minor typo

Greetings,

While reviewing a bit of code around full page images, I came across a
typo and fixed it in the attach.

Sending it here in case anyone feels that we should do more than just
correct the word..?  Perhaps for non-native English speakers seeing
"whose" used here is confusing?

If I don't hear any concerns then I'll go ahead and push it some time
tomorrow; it's a pretty minor change, of course, and we can always
adjust it further if someone raises an issue later too.

Thanks!

Stephen