whisper : fix uninitialized exp_n_audio_ctx

Author: finnvoor

whisper.cpp

@@ -601,7 +601,7 @@ struct whisper_context {
     std::vector<float> energy; // PCM signal energy
 
     // [EXPERIMENTAL] speed-up techniques
-    int32_t exp_n_audio_ctx; // 0 - use default
+    int32_t exp_n_audio_ctx = 0; // 0 - use default
 
     void use_buf(struct ggml_context * ctx, int i) {
 #if defined(WHISPER_USE_SCRATCH)