main : fix std in input (#503)

if we don't add this as an explicit check, then we get an "error: unknown argument: -" later on

examples/main/main.cpp

@@ -91,7 +91,12 @@ void whisper_print_usage(int argc, char ** argv, const whisper_params & params);
 bool whisper_params_parse(int argc, char ** argv, whisper_params & params) {
     for (int i = 1; i < argc; i++) {
         std::string arg = argv[i];
-
+	    
+        if (arg == "-"){
+            params.fname_inp.push_back(arg);
+            continue;
+        }
+	
         if (arg[0] != '-') {
             params.fname_inp.push_back(arg);
             continue;