Windows 2000 optimisation.

Windows 2000 takes a few seconds to time out when trying and failing to
connect to the service manager if NSSM was run with no arguments.

Check for stdin first.  It won't exist if we are running in a service
context so we can skip the connection attempt unless we're unsure.

nssm.cpp

@@ -58,15 +58,28 @@ int main(int argc, char **argv) {
   /* Register messages */
   if (is_admin) create_messages();
 
-  /* Start service magic */
-  SERVICE_TABLE_ENTRY table[] = { { NSSM, service_main }, { 0, 0 } };
-  if (! StartServiceCtrlDispatcher(table)) {
-    unsigned long error = GetLastError();
-    /* User probably ran nssm with no argument */
-    if (error == ERROR_FAILED_SERVICE_CONTROLLER_CONNECT) exit(usage(1));
-    log_event(EVENTLOG_ERROR_TYPE, NSSM_EVENT_DISPATCHER_FAILED, error_string(error), 0);
-    exit(100);
+  /*
+    Optimisation for Windows 2000:
+    When we're run from the command line the StartServiceCtrlDispatcher() call
+    will time out after a few seconds on Windows 2000.  On newer versions the
+    call returns instantly.  Check for stdin first and only try to call the
+    function if there's no input stream found.  Although it's possible that
+    we're running with input redirected it's much more likely that we're
+    actually running as a service.
+    This will save time when running with no arguments from a command prompt.
+  */
+  if (_fileno(stdin) < 0) {
+    /* Start service magic */
+    SERVICE_TABLE_ENTRY table[] = { { NSSM, service_main }, { 0, 0 } };
+    if (! StartServiceCtrlDispatcher(table)) {
+      unsigned long error = GetLastError();
+      /* User probably ran nssm with no argument */
+      if (error == ERROR_FAILED_SERVICE_CONTROLLER_CONNECT) exit(usage(1));
+      log_event(EVENTLOG_ERROR_TYPE, NSSM_EVENT_DISPATCHER_FAILED, error_string(error), 0);
+      exit(100);
+    }
   }
+  else exit(usage(1));
 
   /* And nothing more to do */
   exit(0);