Improve aac decoder selection

src/audio_core/hle/ffmpeg_decoder.cpp

@@ -12,6 +12,9 @@ public:
     explicit Impl(Memory::MemorySystem& memory);
     ~Impl();
     std::optional<BinaryResponse> ProcessRequest(const BinaryRequest& request);
+    bool IsValid() const {
+        return initalized;
+    }
 
 private:
     std::optional<BinaryResponse> Initalize(const BinaryRequest& request);
@@ -261,4 +264,8 @@ std::optional<BinaryResponse> FFMPEGDecoder::ProcessRequest(const BinaryRequest&
     return impl->ProcessRequest(request);
 }
 
+bool FFMPEGDecoder::IsValid() const {
+    return impl->IsValid();
+}
+
 } // namespace AudioCore::HLE