stream : add nullptr check of whisper_context (#3283)

* stream : add nullptr check of whisper_context

This commit adds a check to ensure that the `whisper_context` is not
null after initialization.

The motivation for this is that currently, if the initialization fails,
the program continues to run leading to a segmentation fault. This sort
of check is performed by others examples like whisper-cli.

Refs: https://github.com/ggml-org/whisper.cpp/issues/3280#issuecomment-3003778035

* examples : add nullptr check for whisper_context

examples/bench/bench.cpp

@@ -67,6 +67,10 @@ static int whisper_bench_full(const whisper_params & params) {
     cparams.flash_attn = params.flash_attn;
 
     struct whisper_context * ctx = whisper_init_from_file_with_params(params.model.c_str(), cparams);
+    if (ctx == nullptr) {
+        fprintf(stderr, "error: failed to initialize whisper context\n");
+        return 2;
+    }
 
     {
         fprintf(stderr, "\n");

examples/command/command.cpp

@@ -709,6 +709,10 @@ int main(int argc, char ** argv) {
     cparams.flash_attn = params.flash_attn;
 
     struct whisper_context * ctx = whisper_init_from_file_with_params(params.model.c_str(), cparams);
+    if (ctx == nullptr) {
+        fprintf(stderr, "error: failed to initialize whisper context\n");
+        return 2;
+    }
 
     // print some info about the processing
     {

examples/stream/stream.cpp

@@ -163,6 +163,10 @@ int main(int argc, char ** argv) {
     cparams.flash_attn = params.flash_attn;
 
     struct whisper_context * ctx = whisper_init_from_file_with_params(params.model.c_str(), cparams);
+    if (ctx == nullptr) {
+        fprintf(stderr, "error: failed to initialize whisper context\n");
+        return 2;
+    }
 
     std::vector<float> pcmf32    (n_samples_30s, 0.0f);
     std::vector<float> pcmf32_old;

examples/vad-speech-segments/speech.cpp

@@ -111,6 +111,10 @@ int main(int argc, char ** argv) {
     struct whisper_vad_context * vctx = whisper_vad_init_from_file_with_params(
             cli_params.vad_model.c_str(),
             ctx_params);
+    if (vctx == nullptr) {
+        fprintf(stderr, "error: failed to initialize whisper context\n");
+        return 2;
+    }
 
     // Detect speech in the input audio file.
     if (!whisper_vad_detect_speech(vctx, pcmf32.data(), pcmf32.size())) {