Fix issue with shadow mask + small optim

ScriptableRenderPipeline/Core/CoreRP/ShaderLibrary/Shadow/ShadowAlgorithms.hlsl

 	payloadOffset++;
 		  alpha      = border <= 0.0 ? 0.0 : saturate( (relDistance - (1.0 - border)) / border );
 	real  cascDot    = dot( cascadeDir, wposDir );
-		  alpha      = cascDot > 0.0 ? alpha : lerp( alpha, 0.0, saturate( -cascDot * 4.0 ) );
+		  alpha      = lerp( alpha, 0.0, saturate( -cascDot * 4.0 ) );
 
 	return shadowSplitIndex;
 }

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Lighting/LightEvaluation.hlsl

         int cascadeCount;
         int shadowSplitIndex = EvalShadow_GetSplitIndex(lightLoopContext.shadowContext, lightData.shadowIndex, positionWS, payloadOffset, fade, cascadeCount);
         // we have a fade caclulation for each cascade but we must lerp with shadow mask only for the last one
-        fade = ((shadowSplitIndex + 1) == cascadeCount || shadowSplitIndex == -1.0) ? fade : 0.0;
+        // if shadowSplitIndex is -1 it mean we are outside cascade and should return 1.0 to use shadowmask: saturate(-shadowSplitIndex) return 0 for >= 0 and 1 for -1
+        fade = ((shadowSplitIndex + 1) == cascadeCount) ? fade : saturate(-shadowSplitIndex);
-        // See comment in EvaluateBSDF_Punctual
-        shadow = lightData.nonLightmappedOnly ? min(shadowMask, shadow) : shadow;
+
+        // See comment in EvaluateBSDF_Punctual
+        shadow = lightData.nonLightmappedOnly ? min(shadowMask, shadow) : shadow;
 
         // Note: There is no shadowDimmer when there is no shadow mask
 #endif