Make inventory modifiers move items if there is space available befor…

…e giving up

This means if the size does decrease, you can just remove items then modify it to retrive old ones

src/main/java/slimeknights/tconstruct/library/modifiers/impl/InventoryModifier.java

@@ -18,6 +18,7 @@
 import slimeknights.tconstruct.library.tools.nbt.ModDataNBT;
 
 import javax.annotation.Nullable;
+import java.util.BitSet;
 import java.util.function.BiFunction;
 
 /** Modifier that has an inventory */
@@ -60,12 +61,23 @@ public ValidatedResult validate(IToolStackView tool, int level) {
         if (level == 0) {
           return HAS_ITEMS;
         }
-        // determine the largest index we are using
+        // first, see whether we have any available slots
         int maxSlots = getSlots(tool, level);
+        BitSet freeSlots = new BitSet(maxSlots);
+        freeSlots.set(0, maxSlots-1, true);
+        for (int i = 0; i < listNBT.size(); i++) {
+          freeSlots.set(listNBT.getCompound(i).getInt(TAG_SLOT), false);
+        }
         for (int i = 0; i < listNBT.size(); i++) {
           CompoundTag compoundNBT = listNBT.getCompound(i);
           if (compoundNBT.getInt(TAG_SLOT) >= maxSlots) {
-            return HAS_ITEMS;
+            int free = freeSlots.stream().findFirst().orElse(-1);
+            if (free == -1) {
+              return HAS_ITEMS;
+            } else {
+              freeSlots.set(free, false);
+              compoundNBT.putInt(TAG_SLOT, free);
+            }
           }
         }
       }