Fix mount failed after partition table change

1. xfbint install in partition one and reset partition table, so should partprobe before mount
2. fix crash of empty QStringList get last

tower: https://tower.im/projects/5561a1eca9d14ee2811802983b1b1622/todos/5f7553c18a2746bca443e990ba37d042/

Change-Id: Ib24e84653763178511c63eecadef742b9579c029