fix(@ngtools/webpack): add check for request parameter

[sumbad]

I use my own webpack config with @ngtools/webpack plugin and I have got an error during compiling.

Error log

[0] building modulesℹ ｢wds｣: Project is running at http://localhost:8080/
ℹ ｢wds｣: webpack output is served from /
ℹ ｢wds｣: Content not from webpack is served from /home/dsumbaev/DEVELOPMENT/bill-client-front/dist
ℹ ｢wds｣: 404s will fallback to /index.html
[0] building modules/home/dsumbaev/DEVELOPMENT/bill-client-front/node_modules/@ngtools/webpack/src/angular_compiler_plugin.js:509
                    if (this.done && (request.request.endsWith('.ts')
                                              ^

TypeError: Cannot read property 'request' of null
    at nmf.hooks.beforeResolve.tapAsync (/home/dsumbaev/DEVELOPMENT/bill-client-front/node_modules/@ngtools/webpack/src/angular_compiler_plugin.js:509:47)
    at _fn1 (eval at create (/home/dsumbaev/DEVELOPMENT/bill-client-front/node_modules/webpack/node_modules/tapable/lib/HookCodeFactory.js:24:12), <anonymous>:27:1)
    at Object.resolveWithPaths (/home/dsumbaev/DEVELOPMENT/bill-client-front/node_modules/@ngtools/webpack/src/paths-plugin.js:14:9)
    at nmf.hooks.beforeResolve.tapAsync (/home/dsumbaev/DEVELOPMENT/bill-client-front/node_modules/@ngtools/webpack/src/angular_compiler_plugin.js:521:32)
    at AsyncSeriesWaterfallHook.eval [as callAsync] (eval at create (/home/dsumbaev/DEVELOPMENT/bill-client-front/node_modules/webpack/node_modules/tapable/lib/HookCodeFactory.js:24:12), <anonymous>:19:1)
    at NormalModuleFactory.create (/home/dsumbaev/DEVELOPMENT/bill-client-front/node_modules/webpack/lib/NormalModuleFactory.js:338:28)
    at semaphore.acquire (/home/dsumbaev/DEVELOPMENT/bill-client-front/node_modules/webpack/lib/Compilation.js:494:14)
    at Semaphore.acquire (/home/dsumbaev/DEVELOPMENT/bill-client-front/node_modules/webpack/lib/util/Semaphore.js:17:4)
    at asyncLib.forEach (/home/dsumbaev/DEVELOPMENT/bill-client-front/node_modules/webpack/lib/Compilation.js:492:15)
    at arrayEach (/home/dsumbaev/DEVELOPMENT/bill-client-front/node_modules/neo-async/async.js:2400:9)
    at Object.each (/home/dsumbaev/DEVELOPMENT/bill-client-front/node_modules/neo-async/async.js:2835:9)
    at Compilation.addModuleDependencies (/home/dsumbaev/DEVELOPMENT/bill-client-front/node_modules/webpack/lib/Compilation.js:471:12)
    at Compilation.processModuleDependencies (/home/dsumbaev/DEVELOPMENT/bill-client-front/node_modules/webpack/lib/Compilation.js:450:8)
    at afterBuild (/home/dsumbaev/DEVELOPMENT/bill-client-front/node_modules/webpack/lib/Compilation.js:556:15)
    at buildModule.err (/home/dsumbaev/DEVELOPMENT/bill-client-front/node_modules/webpack/lib/Compilation.js:600:11)
    at callback (/home/dsumbaev/DEVELOPMENT/bill-client-front/node_modules/webpack/lib/Compilation.js:358:35)

This PR address to fix the issue #880.

[filipesilva]

LGTM, thanks for fixing this 👍