Cast natural light regardless of brightness

Previously, natural light was only cast onto walls and into buildings
during the day.  This had strange side-effects, like walls being almost
invisible at night.

Remove that check and simply always cast the light.

Fixes CleverRaven#13786

src/lightmap.cpp

@@ -224,7 +224,7 @@ void map::generate_lightmap( const int zlev )
                     const int y = sy + smy * SEEY;
                     const tripoint p( x, y, zlev );
                     // Project light into any openings into buildings.
-                    if( natural_light > LIGHT_SOURCE_BRIGHT && !outside_cache[p.x][p.y] ) {
+                    if( !outside_cache[p.x][p.y] ) {
                         // Apply light sources for external/internal divide
                         for( int i = 0; i < 4; ++i ) {
                             if( INBOUNDS( p.x + dir_x[i], p.y + dir_y[i] ) &&