Cordova support: Check for existence of Symbol.for

Fixes: feross/buffer#241

See: feross/buffer#204 (comment)

Author: feross

index.js

@@ -10,7 +10,10 @@
 
 var base64 = require('base64-js')
 var ieee754 = require('ieee754')
-var customInspectSymbol = typeof Symbol === 'function' ? Symbol.for('nodejs.util.inspect.custom') : null
+var customInspectSymbol =
+  (typeof Symbol === 'function' && typeof Symbol.for === 'function')
+    ? Symbol.for('nodejs.util.inspect.custom')
+    : null
 
 exports.Buffer = Buffer
 exports.SlowBuffer = SlowBuffer