libretro: Make single cards for playlist the default, fix disabled case

This bug was causing the option to act as if it was disabled anyway.

src/core/system.cpp

@@ -392,7 +392,7 @@ bool Boot(const SystemBootParameters& params)
   }
 
   // Notify change of disc.
-  UpdateRunningGame(params.filename.c_str(), media.get());
+  UpdateRunningGame(media ? media->GetFileName().c_str() : params.filename.c_str(), media.get());
   UpdateControllers();
   UpdateMemoryCards();
   Reset();

src/duckstation-libretro/libretro_host_interface.cpp

@@ -520,7 +520,7 @@ static std::array<retro_core_option_definition, 30> s_option_definitions = {{
    "When using a playlist (m3u) and per-game (title) memory cards, a single memory card "
    "will be used for all discs. If unchecked, a separate card will be used for each disc.",
    {{"true", "Enabled"}, {"false", "Disabled"}},
-   "false"},
+   "true"},
   {"duckstation_Controller1.Type",
    "Controller 1 Type",
    "Sets the type of controller for Slot 1.",