fix crash with ME bridge when ae2things not present

close #829

Author: zyxkad

src/main/java/de/srendi/advancedperipherals/common/addons/ae2/AEApi.java

@@ -855,7 +855,7 @@ static ICellWrapper of(Item item, ItemStack stack) {
             if (item instanceof IBasicCellItem cell) {
                 return new BasicCellWrapper(cell, stack);
             }
-            if (item instanceof IDISKCellItem cell) {
+            if (APAddon.AE2THINGS.isLoaded() && item instanceof IDISKCellItem cell) {
                 return new AE2ThingsDiskCellWrapper(cell, stack);
             }
             if (item instanceof AEDiskCellItem cell) {