Compare arrays properly

Don't know which method is the most tasteful in this case so I just went with the one I already knew

core/field_dropdown.js

@@ -164,7 +164,7 @@ Blockly.FieldDropdown.prototype.init = function() {
  */
 Blockly.FieldDropdown.prototype.showEditor_ = function() {
   var options = this.getOptions();
-  if (options.length == 0 || options == ['']) return;
+  if (options.length == 0 || JSON.stringify(options) === '[""]') return;
 
   this.dropDownOpen_ = true;
   // If there is an existing drop-down someone else owns, hide it immediately and clear it.