Validate input sid (#369)

sherpa-onnx/csrc/offline-tts-vits-impl.h

@@ -25,6 +25,23 @@ class OfflineTtsVitsImpl : public OfflineTtsImpl {
 
   GeneratedAudio Generate(const std::string &text,
                           int64_t sid = 0) const override {
+    int32_t num_speakers = model_->NumSpeakers();
+    if (num_speakers == 0 && sid != 0) {
+      SHERPA_ONNX_LOGE(
+          "This is a single-speaker model and supports only sid 0. Given sid: "
+          "%d",
+          sid);
+      return {};
+    }
+
+    if (num_speakers != 0 && (sid >= num_speakers || sid < 0)) {
+      SHERPA_ONNX_LOGE(
+          "This model contains only %d speakers. sid should be in the range "
+          "[%d, %d]. Given: %d",
+          num_speakers, 0, num_speakers - 1, sid);
+      return {};
+    }
+
     std::vector<int64_t> x = lexicon_.ConvertTextToTokenIds(text);
     if (x.empty()) {
       SHERPA_ONNX_LOGE("Failed to convert %s to token IDs", text.c_str());