Resolves#12795
After the Color Space Invasion, gimp_gradient_get_uniform_samples ()
returns an array of GeglColors rather than GimpRGB values and a status
variable. This patch fixes the Spyro-Plus plug-in to expects the new
return values.
It also restores code that utilized the second color gradient in the output
when the Gradient's Repeat Mode is Triangular Wave. This appears to
have been lost during the port from GIMP 2.10.
eb8076526d