Fix crash when invalidating invalid network elements

This could occur when using AE2's Spatial IO.

Closes #1410

src/main/java/org/cyclops/integrateddynamics/core/network/PartNetworkElement.java

@@ -89,7 +89,7 @@ public IPartContainer getPartContainer() {
     }
 
     public Optional<IPartContainer> getPartContainerOptional() {
-        return PartHelpers.getPartContainer(getCenterPos(getTarget()), getTarget().getCenter().getSide());
+        return PartHelpers.getPartContainer(this.center.getPos(), this.center.getSide());
     }
 
     @Override