Fix at_midBlock at high coordinates (#1949)

src/main/java/net/coderbot/iris/vertices/ExtendedDataHelper.java

@@ -12,9 +12,9 @@ public final class ExtendedDataHelper {
 
 	public static int computeMidBlock(float x, float y, float z, int localPosX, int localPosY, int localPosZ) {
 		return packMidBlock(
-				localPosX + 0.5f - x,
-				localPosY + 0.5f - y,
-				localPosZ + 0.5f - z
+            (localPosX & 0xFFFF) + 0.5f - x,
+			(localPosY & 0xFFFF) + 0.5f - y,
+			(localPosZ & 0xFFFF) + 0.5f - z
 		);
 	}
 }