Change ENUMBRANCE_UPDATE item flag to boolean member:

This means:
- it's ignored when comparing items (items with the flag stack together with items that don't have the flag),
- it's not saved, it's temporary anyway.

src/character.cpp

@@ -1266,10 +1266,10 @@ void Character::check_item_encumbrance_flag()
 {
     bool update_required = check_encumbrance;
     for( auto &i : worn ) {
-        if( !update_required && i.has_flag( "ENCUMBRANCE_UPDATE" ) ) {
+        if( !update_required && i.encumbrance_update_ ) {
             update_required = true;
         }
-        i.unset_flag( "ENCUMBRANCE_UPDATE" );
+        i.encumbrance_update_ = false;
     }
 
     if( update_required ) {

src/item.cpp

@@ -3697,7 +3697,7 @@ void item::on_contents_changed()
         convert( type->container->unseals_into );
     }
 
-    set_flag( "ENCUMBRANCE_UPDATE" );
+    encumbrance_update_ = true;
 }
 
 void item::on_damage( int, damage_type )

src/item.h

@@ -2138,6 +2138,11 @@ class item : public visitable<item>
         int mission_id = -1;       // Refers to a mission in game's master list
         int player_id = -1;        // Only give a mission to the right player!
 
+        // Set when the item / its content changes. Used for worn item with
+        // encumbrance depending on their content.
+        // This not part serialized or compared on purpose!
+        bool encumbrance_update_ = false;
+
     private:
         /**
          * Accumulated rot, expressed as time the item has been in standard temperature.

src/player.cpp

@@ -3318,10 +3318,10 @@ void player::process_items()
         } else if( identifier == "adv_UPS_off" ) {
             ch_UPS += w.ammo_remaining() / 0.6;
         }
-        if( !update_required && w.has_flag( "ENCUMBRANCE_UPDATE" ) ) {
+        if( !update_required && w.encumbrance_update_ ) {
             update_required = true;
         }
-        w.unset_flag( "ENCUMBRANCE_UPDATE" );
+        w.encumbrance_update_ = false;
     }
     if( update_required ) {
         reset_encumbrance();