Fix stacks losing empty attr modifiers

Fixes #10686

patches/server/General-ItemMeta-fixes.patch

@@ -288,12 +288,14 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
              this.displayName = component;
          });
 @@ -0,0 +0,0 @@ class CraftMetaItem implements ItemMeta, Damageable, Repairable, BlockDataMeta {
+     }
  
      void applyModifiers(Multimap<Attribute, AttributeModifier> modifiers, CraftMetaItem.Applicator tag) {
-         if (modifiers == null || modifiers.isEmpty()) {
+-        if (modifiers == null || modifiers.isEmpty()) {
 -            if (this.hasItemFlag(ItemFlag.HIDE_ATTRIBUTES)) {
 -                tag.put(CraftMetaItem.ATTRIBUTES, new ItemAttributeModifiers(Collections.emptyList(), false));
 -            }
++        if (modifiers == null/* || modifiers.isEmpty()*/) { // Paper - empty modifiers has a specific meaning, they should still be saved
 +            // Paper - don't save ItemFlag if the underlying data isn't present
              return;
          }