Fix legacy DFU porting typo. (#2744)

Only affected fabric/(neo)forge but didn't get hit for 6 years apparently.

Author: wizjany

worldedit-fabric/src/main/java/com/sk89q/worldedit/fabric/FabricDataFixer.java

@@ -595,7 +595,7 @@ private static void convertItems(net.minecraft.nbt.CompoundTag nbttagcompound, S
             ListTag nbttaglist = nbttagcompound.getList(key, 10);
 
             for (int j = 0; j < nbttaglist.size(); ++j) {
-                nbttaglist.add(j, convert(LegacyType.ITEM_INSTANCE, nbttaglist.getCompound(j), sourceVer, targetVer));
+                nbttaglist.set(j, convert(LegacyType.ITEM_INSTANCE, nbttaglist.getCompound(j), sourceVer, targetVer));
             }
         }
 

worldedit-neoforge/src/main/java/com/sk89q/worldedit/neoforge/NeoForgeDataFixer.java

@@ -595,7 +595,7 @@ private static void convertItems(net.minecraft.nbt.CompoundTag nbttagcompound, S
             ListTag nbttaglist = nbttagcompound.getList(key, 10);
 
             for (int j = 0; j < nbttaglist.size(); ++j) {
-                nbttaglist.add(j, convert(LegacyType.ITEM_INSTANCE, nbttaglist.getCompound(j), sourceVer, targetVer));
+                nbttaglist.set(j, convert(LegacyType.ITEM_INSTANCE, nbttaglist.getCompound(j), sourceVer, targetVer));
             }
         }