Fixed previous progress with linear cubic bezier (#494)

* Fixed previous progress with linear cb

Co-authored-by: aborziak-ms <[email protected]>

Author: FrayxRulez

source/LottieToWinComp/Animate.cs

@@ -682,7 +682,15 @@ static void GenericCreateCompositionKeyFrameAnimation<TCA, T>(
                         {
                             // Ensure the previous expression doesn't continue being evaluated during the current keyframe.
                             // This is necessary because the expression is only defined from the previous progress to the current progress.
-                            InsertKeyFrame(compositionAnimation, currentProgress, previousValue, context.ObjectFactory.CreateStepThenHoldEasingFunction());
+                            var nextLargerThanPrevious = Float32.NextLargerThan(previousProgress);
+                            InsertKeyFrame(compositionAnimation, nextLargerThanPrevious, previousValue, context.ObjectFactory.CreateStepThenHoldEasingFunction());
+
+                            if (currentProgress <= nextLargerThanPrevious)
+                            {
+                                // Prevent the next key frame from being inserted at the same progress value
+                                // as the one we just inserted.
+                                currentProgress = Float32.NextLargerThan(nextLargerThanPrevious);
+                            }
                         }
 
                         // The easing for a keyframe at 0 is unimportant, so always use Hold.