New logic for connections to memorized tiles

Previously when a tile was memorized we used the memorized terrain type
to determine whether it was in the connect_group of interest.

However, that doesn't always work, because the memorized tile might be
furniture or vehicle instead.  Also, it doesn't work for curses because
we don't have the tile type at all, only the symbol, from which we
cannot reverse-engineer what connect_groups it belonged to.

The new approach is that if a tile is memorized at all, we assume you
know the true terrain type.  This fails in other situations; you will
now magically know when a wall collapses even if you don't see the new
terrain, but it is less problematic overall.

src/map.cpp

@@ -1343,25 +1343,25 @@ uint8_t map::get_known_connections( const tripoint &p, int connect_group ) const
     bool is_transparent =
         ch.transparency_cache[p.x][p.y] > LIGHT_TRANSPARENCY_SOLID;
     uint8_t val = 0;
+    auto const is_memorized =
+    [&]( const tripoint & q ) {
+        return !g->u.get_memorized_tile( getabs( q ) ).tile.empty();
+    };
 
     // populate connection information
     for( int i = 0; i < 4; ++i ) {
         tripoint neighbour = p + offsets[i];
         if( !inbounds( neighbour ) ) {
             continue;
         }
-        const ter_t *neighbour_terrain = nullptr;
-        if( is_transparent || ch.visibility_cache[neighbour.x][neighbour.y] <= LL_BRIGHT ) {
-            neighbour_terrain = &ter( neighbour ).obj();
-        } else {
-            ter_str_id t_id( g->u.get_memorized_tile( getabs( neighbour ) ).tile );
-            if( t_id.is_valid() ) {
-                neighbour_terrain = &t_id.obj();
+        if( is_transparent ||
+            ch.visibility_cache[neighbour.x][neighbour.y] <= LL_BRIGHT ||
+            is_memorized( neighbour ) ) {
+            const ter_t &neighbour_terrain = ter( neighbour ).obj();
+            if( neighbour_terrain.connects_to( connect_group ) ) {
+                val += 1 << i;
             }
         }
-        if( neighbour_terrain && neighbour_terrain->connects_to( connect_group ) ) {
-            val += 1 << i;
-        }
     }
 
     return val;