Fix bugs of depth backward pass

Author: ingra14m

Diff for: cuda_rasterizer/backward.cu

@@ -453,10 +453,11 @@ renderCUDA(
 	float dL_dpixel[C];
 	float dL_depth;
 	float accum_depth_rec = 0;
-	if (inside)
+	if (inside){
 		for (int i = 0; i < C; i++)
 			dL_dpixel[i] = dL_dpixels[i * H * W + pix_id];
 	        dL_depth = dL_depths[pix_id];
+	}
 
 	float last_alpha = 0;
 	float last_color[C] = { 0 };