fix segfault during shell nandroid backup/restore commands

Previously, to achieve a successful "adb shell nandroid backup" and
"adb shell nandroid restore [backup_path]", we have to disable
progress bar by manually removing '/sdcard/clockworkmod/.hidenandroidprogress'

Else, the recovery would crash with segfault

This patch disables progress bar update whenever ui is not initialized
adb shell nandroid backup/restore commands now work without any background hack

Change-Id: I525ceffffb1bad4ee8e62c3985e123dcda77c79e