fixed bug in blurred shadow related to checking if MAIN_LIGHT_CALCULATE_SHADOWS is defined producing a full black plane

Assets/Shaders/Shadows/ShaderGraphs/BlurredShadowPlaneLighting.hlsl

 #else
 		half cascadeIndex = 0;
 #endif
+#if !defined(MAIN_LIGHT_CALCULATE_SHADOWS)
+		float shadowMapSample = 1.0;
+#else
+#endif		
-		float isInShadow = step(shadowMapSample, shadowCoord.z);
+		float isInShadow = 1 - shadowMapSample;
 
 		shadowAtten -= isInShadow * oneDivNumSteps;
 		// If the position is out of shadow distance, just return 1