Use 'var' for ENVIRONMENT_IS_PTHREAD in src/shell.js.

Author: juj

src/shell.js

@@ -42,7 +42,8 @@ var ENVIRONMENT_IS_WEB = typeof window === 'object';
 // 3) We could be an application pthread running in a worker. (ENVIRONMENT_IS_WORKER == true and ENVIRONMENT_IS_PTHREAD == true)
 var ENVIRONMENT_IS_WORKER = typeof importScripts === 'function';
 #if USE_PTHREADS
-if (typeof ENVIRONMENT_IS_PTHREAD === 'undefined') ENVIRONMENT_IS_PTHREAD = false; // ENVIRONMENT_IS_PTHREAD=true will have been preset in pthread-main.js.
+var ENVIRONMENT_IS_PTHREAD;
+if (!ENVIRONMENT_IS_PTHREAD) ENVIRONMENT_IS_PTHREAD = false; // ENVIRONMENT_IS_PTHREAD=true will have been preset in pthread-main.js. Make it false in the main runtime thread.
 #endif
 var ENVIRONMENT_IS_SHELL = !ENVIRONMENT_IS_WEB && !ENVIRONMENT_IS_NODE && !ENVIRONMENT_IS_WORKER;