stream : support language auto-detect (#501)

#445 fix Language auto-detect "auto" flag does not work using the stream tool

examples/stream/stream.cpp

@@ -148,7 +148,7 @@ int main(int argc, char ** argv) {
 
     // whisper init
 
-    if (whisper_lang_id(params.language.c_str()) == -1) {
+    if (params.language != "auto" && whisper_lang_id(params.language.c_str()) == -1){
         fprintf(stderr, "error: unknown language '%s'\n", params.language.c_str());
         whisper_print_usage(argc, argv, params);
         exit(0);