Fix #1446217 - Fix potential crash when rendering gradients.
Fix #1446217 - Fix potential crash when rendering gradients.

Enumerable.Range takes the start index and a count, not the start index
and end index.

jakeclawson/Pinta,Fenex/Pinta,Fenex/Pinta,PintaProject/Pinta,jakeclawson/Pinta,PintaProject/Pinta,PintaProject/Pinta,Mailaender/Pinta,Mailaender/Pinta