Fix furniture being "destroyed" when grab-moving (#47457)

src/game.cpp

@@ -10520,7 +10520,7 @@ bool game::grabbed_furn_move( const tripoint &dp )
 
     // Actually move the furniture.
     m.furn_set( fdest, m.furn( fpos ) );
-    m.furn_set( fpos, f_null );
+    m.furn_set( fpos, f_null, true );
 
     if( fire_intensity == 1 && !pulling_furniture ) {
         m.remove_field( fpos, fd_fire );

src/map.cpp

@@ -1331,7 +1331,7 @@ furn_id map::furn( const tripoint &p ) const
     return current_submap->get_furn( l );
 }
 
-void map::furn_set( const tripoint &p, const furn_id &new_furniture )
+void map::furn_set( const tripoint &p, const furn_id &new_furniture, const bool furn_reset )
 {
     if( !inbounds( p ) ) {
         return;
@@ -1358,6 +1358,7 @@ void map::furn_set( const tripoint &p, const furn_id &new_furniture )
     avatar &player_character = get_avatar();
     // If player has grabbed this furniture and it's no longer grabbable, release the grab.
     if( player_character.get_grab_type() == object_type::FURNITURE &&
+        !furn_reset &&
         player_character.pos() + player_character.grab_point == p && !new_t.is_movable() ) {
         add_msg( _( "The %s you were grabbing is destroyed!" ), old_t.name() );
         player_character.grab( object_type::NONE );

src/map.h

@@ -688,7 +688,11 @@ class map
         furn_id furn( const point &p ) const {
             return furn( tripoint( p, abs_sub.z ) );
         }
-        void furn_set( const tripoint &p, const furn_id &new_furniture );
+        /**
+        * furn_reset should be true if new_furniture is being set to f_null
+        * when the player is grab-moving furniture
+        */
+        void furn_set( const tripoint &p, const furn_id &new_furniture, bool furn_reset = false );
         void furn_set( const point &p, const furn_id &new_furniture ) {
             furn_set( tripoint( p, abs_sub.z ), new_furniture );
         }