Defensively verify that Symbol.for is available (#2009)

closes #2007

Author: jaynetics

src/jsutils/nodejsCustomInspectSymbol.js

@@ -1,7 +1,7 @@
 // @flow strict
 
 const nodejsCustomInspectSymbol =
-  typeof Symbol === 'function'
+  typeof Symbol === 'function' && typeof Symbol.for === 'function'
     ? Symbol.for('nodejs.util.inspect.custom')
     : undefined;