Fix async loader finish condition check.
Fix async loader finish condition check.

- Both queue_ & done_ needs to be finished to finalize the loader.
  This was making occasional load error in imgui sample project.

Change-Id: I42af34b6d2ef1aa9f4fd608ae3f5e161b504794c

google/fplbase,google/fplbase,google/fplbase,google/fplbase