am 7a013f96: Fix vold coredump when enable_ums cmd comes without media inserted.

Merge commit '7a013f967e6b6fdb3e7e2d46455cdf235ab4472e' into eclair-plus-aosp

* commit '7a013f967e6b6fdb3e7e2d46455cdf235ab4472e':
  Fix vold coredump when enable_ums cmd comes without media inserted.