[BUGFIX] Catch InvalidPackageManifestException in PackageManager

Prevents TYPO3 from going fatal when ext_emconf.php for some
package is missing.

Releases: master
Resolves: #68082
Change-Id: I646a26e9b952561480241cc06ad918fb64bb3d94
Reviewed-on: http://review.typo3.org/41171


Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>