YUIDoc can crash when @file tag is followed by @class tag

[roipoussiere]

When building the documentation from a folder containing only this js file:

/**
 * @file test.js
 * @class The foo class.
 */
function foo() { return 'bar'; }

YUIDoc crashs with this stacktrace:

info: Starting YUIDoc@0.10.2 using YUI@3.18.1 with NodeJS@4.4.7
info: Scanning for yuidoc.json file.
info: Starting YUIDoc with the following options:
info: {"port":3000,"nocode":false,"paths":["."],"outdir":"./out"}
info: YUIDoc Starting from: .
error: --------------------------------------------------------------------------
error: An uncaught YUIDoc error has occurred, stack trace given below
error: --------------------------------------------------------------------------
error: TypeError: Cannot read property 'classes' of undefined
    at null.<anonymous> (/usr/lib/node_modules/yuidocjs/lib/docparser.js:1499:38)
    at Function.O.each (/usr/lib/node_modules/yuidocjs/node_modules/yui/yui-nodejs/yui-nodejs.js:3309:16)
    at a (/usr/lib/node_modules/yuidocjs/node_modules/yui/oop/oop-min.js:1:319)
    at e.each (/usr/lib/node_modules/yuidocjs/node_modules/yui/oop/oop-min.js:1:1249)
    at Y.extend.transform (/usr/lib/node_modules/yuidocjs/lib/docparser.js:1483:15)
    at Y.extend.parse (/usr/lib/node_modules/yuidocjs/lib/docparser.js:1573:25)
    at Object.Y.YUIDoc.run (/usr/lib/node_modules/yuidocjs/lib/yuidoc.js:399:16)
    at Object.<anonymous> (/usr/lib/node_modules/yuidocjs/lib/cli.js:36:40)
    at Module._compile (module.js:409:26)
    at Object.Module._extensions..js (module.js:416:10)
error: --------------------------------------------------------------------------
error: Node.js version: v4.4.7
error: YUI version: 3.18.1
error: YUIDoc version: 0.10.2
error: Please file all tickets here: http://github.com/yui/yuidoc/issues
error: --------------------------------------------------------------------------

Note that YUIDoc do not crash with the following file content (tags have been reversed):

/**
 * @class The foo class.
 * @file test.js
 */
function foo() { return 'bar'; }