[Translation] Make IcuDatFileLoader/IcuResFileLoader::load invalid resource compatible with HHVM.

[Translation] HHVM throws when an invalid ResourceBundle is constructed, while zend returns FALSE from the constructor. This patch makes IcuResFileLoader and IcuDatFileLoader compatible with HHVM.

The following tests now pass on HHVM:
https://github.com/symfony/symfony/blob/2.3/src/Symfony/Component/Translation/Tests/Loader/IcuDatFileLoaderTest.php#L33
https://github.com/symfony/symfony/blob/2.3/src/Symfony/Component/Translation/Tests/Loader/IcuResFileLoaderTest.php#L54

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | N/A
| License       | MIT
| Doc PR        | N/A