bug fix: uncaught error within TranslateService.use()

[sagittarius-rev]

When use the use() method of TranslateService to load an invalid language, it will result nothing. For example, the file assets/i18n/vvvv.json does not exist, so the "vvvv" language is invalid:

this.translateService.use('vvvv').pipe(
  mapTo(true),
  catchError(() => Observable.of(false)),
).subscribe((isSuccess: boolean) => console.warn('isSuccess: ', isSuccess));

The code above will not output anything.

Because there is an uncaught error within the use() method:

      pending.pipe(take(1))
        .subscribe((res: any) => {
          this.changeLang(lang);
        });

If the language file is missing, this code will break the running, the other subscribers of pending will be halt, missing the data of next(), error() or complete().

Adding a void error handler will fix this bug.

[ocombe]

Hello, could you rebase your PR and add a test for that change please? thanks