shell: validate get_animation_type parameter
shell: validate get_animation_type parameter

Signed-off-by: U. Artie Eoff <32aece0d55055227b44d04b7d0051cf3d04ee871@intel.com>

jonnylamb/weston,udoprog/weston,krezovic/weston,kwm81/weston,Gnurou/weston,Gnurou/weston,krezovic/weston,kwm81/weston,Fantu/compositor-spice,udoprog/weston,sir-murray/weston,Tarnyko/weston-xdg_surface_present,Fantu/compositor-spice,giucam/weston,xorgy/weston,Fantu/compositor-spice,xorgy/weston,Tarnyko/weston-xdg_surface_present,jonnylamb/weston,mchalupa/weston,giucam/weston,eyolfson/weston,mchalupa/weston,eyolfson/weston,sir-murray/weston