Fluidsynth: Exhaust the internal synth buffer to prevent playing of o…

…ld samples after long pauses

Fix #3135 (this time for real)

src/decoder_fluidsynth.cpp

@@ -214,7 +214,12 @@ FluidSynthDecoder::~FluidSynthDecoder() {
 	--instances;
 	assert(instances >= 0);
 
-	if (!use_global_synth) {
+	if (use_global_synth) {
+		// Exhaust the internal synth buffer
+		// Prevents that old samples play when a new Midi song starts (even when there was a longer break between them)
+		std::array<uint8_t, 64 * 4> buffer;
+		fluid_synth_write_s16(global_synth.get(), buffer.size() / 4, buffer.data(), 0, 2, buffer.data(), 1, 2);
+	} else {
 		delete_fluid_synth(local_synth);
 	}
 }