ngs2: let CLEAR reopen a closed waveform block list

Co-authored-by: Phr3d13 <phr3d13@gmail.com>

src/libs/ngs2.cpp

@@ -713,10 +713,11 @@ struct Ngs2VoiceInternal {
 		if (count > capacity) {
 			return NGS2_ERROR_INVALID_NUM_WAVEFORM_BLOCKS;
 		}
-		EXIT_NOT_IMPLEMENTED(!accepts_blocks || (flags & ~0x17u) != 0);
 		const bool clear     = (flags & 4u) != 0;
 		const bool only_data = (flags & 2u) != 0;
 		const bool join      = only_data && (flags & 0x10u) == 0;
+		// CLEAR reopens a list that the previous addition closed.
+		EXIT_NOT_IMPLEMENTED((!accepts_blocks && !clear) || (flags & ~0x17u) != 0);
 		const auto retained = clear ? 0 : blocks.size();
 		Block      tail     = retained == 0 ? Block {} : blocks.back();
 		std::vector<Block> pending;

tests/Ngs2SamplerTests.cpp

@@ -1210,6 +1210,15 @@ void TestDeferredSamplerSetup() {
 	      "sampler did not play after deferred stream setup");
 }
 
+void TestClearReopensClosedList() {
+	Fixture       f(48000);
+	const int16_t first = 8192, second = -16384;
+	f.Queue(&first, 1, 0);
+	f.Queue(&second, 1, 4);
+	f.Render(1);
+	Check(f.voice.samples[0] == -0.5f, "CLEAR did not reopen a closed waveform list");
+}
+
 void TestSetupQuery() {
 	Fixture  f(48000, 2);
 	uint32_t info[2] = {99, 99};
@@ -1965,6 +1974,7 @@ int main() {
 	TestDefaultMatrix();
 	TestMatrixOutputChannels();
 	TestCustomPcmStillPlays();
+	TestClearReopensClosedList();
 	TestSetupQuery();
 	TestPortInfo();
 	TestPlayStateBeforeRender();