[BUGFIX] PackageManager fails on empty array entries in conflicts

Use the same solution as depends some lines above, skip those entries.

Resolves: #52753
Releases: 6.2
Change-Id: Icd7b154be90afe11e9e19dac70ee78eb09a6d1dd
Reviewed-on: https://review.typo3.org/24698
Reviewed-by: Thomas Maroschik
Tested-by: Thomas Maroschik
Reviewed-by: Ernesto Baschny
Tested-by: Ernesto Baschny
Reviewed-by: Xavier Perseguers
Reviewed-by: Helmut Hummel
Tested-by: Helmut Hummel