Add warning to blockToCode (#4492)

* Add warning to blockToCode

* Address PR comments

generators/php.js

@@ -117,6 +117,12 @@ Blockly.PHP.ORDER_OVERRIDES = [
   [Blockly.PHP.ORDER_LOGICAL_OR, Blockly.PHP.ORDER_LOGICAL_OR]
 ];
 
+/**
+ * Whether the init method has been called.
+ * @type {?boolean}
+ */
+Blockly.PHP.isInitialized = false;
+
 /**
  * Initialise the database of variable names.
  * @param {!Blockly.Workspace} workspace Workspace to generate code from.
@@ -154,6 +160,7 @@ Blockly.PHP.init = function(workspace) {
 
   // Declare all of the variables.
   Blockly.PHP.definitions_['variables'] = defvars.join('\n');
+  this.isInitialized = true;
 };
 
 /**