Pad: Use memory card filename from current state

Fixes memory card data getting lost after loading state.

src/core/memory_card.h

@@ -19,6 +19,8 @@ public:
   static std::unique_ptr<MemoryCard> Open(std::string_view filename);
 
   const MemoryCardImage::DataArray& GetData() const { return m_data; }
+  const std::string& GetFilename() const { return m_filename; }
+  void SetFilename(std::string filename) { m_filename = std::move(filename); }
 
   void Reset();
   bool DoState(StateWrapper& sw);

src/core/pad.cpp

@@ -110,6 +110,7 @@ bool Pad::DoState(StateWrapper& sw)
         if (m_memory_cards[i]->GetData() == card_from_state->GetData())
         {
           Log_DevPrintf("Using memory card %u state from save state", i);
+          card_from_state->SetFilename(m_memory_cards[i]->GetFilename());
           m_memory_cards[i] = std::move(card_from_state);
         }
         else