Stop using validcount for sprites

src/swrenderer/things/r_visiblesprite.cpp

@@ -77,6 +77,10 @@ namespace swrenderer
 		if (x1 >= x2)
 			return;
 
+		// Reject sprites outside the slice rendered by the thread
+		if (x2 < thread->X1 || x1 > thread->X2)
+			return;
+
 		// [RH] Sprites split behind a one-sided line can also be discarded.
 		if (spr->sector == nullptr)
 			return;