Fix enabling slideshow controls
Fix enabling slideshow controls

Set slideshow controls enabled only when adding the first frame. This
fixes a minor bug where they could be enabled while the slideshow is
inactive (when they are supposed to be disabled) if data is loaded while
the slideshow is active.

linus-sherrill/maptk,linus-sherrill/maptk,linus-sherrill/maptk,linus-sherrill/maptk,linus-sherrill/maptk