`hasWindowDefined` can be `true` value in SSR.

Hello. I found some errors in SSR and its root cause is came from ngx-infinite-scroll

To compatible with many libraries in SSR, we use 'jsdom' to mocking window object in Node JS Environment. It means we inject window variable in global variable like this.

const jsdom = require('jsdom');
const win = new jsdom.JSDOM(template);
global['window'] = win.window;

In Angular Universal, they recommends to inject window object to pass compile with using many 3rd party libraries. So, it is common use-case for angular user.

Here is the error i found.

ERROR TypeError: Cannot read property 'documentElement' of undefined
    at getDocumentElement (/.../dist-mobile/server/37.js:4535:53)
    at getElementHeight (/.../dist-mobile/server/37.js:4603:21)
    at calculatePointsForWindow (/.../dist-mobile/server/37.js:4556:31)
    at calculatePoints (/.../dist-mobile/server/37.js:4540:30)
    at createScroller (/.../dist-mobile/server/37.js:4766:20)
    at /.../dist-mobile/server/37.js:4888:32
    at _ZoneDelegate.invoke (/.../dist-mobile/server/main.js:146416:26)
    at Zone.run (/.../dist-mobile/server/main.js:146178:43)
    at NgZone.runOutsideAngular (/.../dist-mobile/server/main.js:228518:28)
    at InfiniteScrollDirective.setup (/.../dist-mobile/server/37.js:4887:17)
    at InfiniteScrollDirective.ngAfterViewInit (/.../dist-mobile/server/37.js:4862:12)
    at callHook (/.../dist-mobile/server/main.js:205613:22)
    at callHooks (/.../dist-mobile/server/main.js:205582:17)

https://github.com/orizens/ngx-infinite-scroll/blob/master/projects/ngx-infinite-scroll/src/lib/ngx-infinite-scroll.directive.ts#L73 I think it can be fixed with checking isPlatformBrowser in here.

  setup() {
    if (hasWindowDefined()) {

to be

  setup() {
    if (hasWindowDefined() && isPlatformBrowser(this.platformId)) {

orizens / ngx-infinite-scroll

`hasWindowDefined` can be `true` value in SSR. #397