[AssetAtlas]: Fix AssetAtlas not consider all size of texture.

Symptom:
Atlas service get exception because the result is null.

Root Cause:
The original logic will miss the largest width in each thread.
Take two processors as an example, first thread will miss 2048, second thread will miss 1984.
With some condition, only 2048*2048 or 1984*2048 can exceed the mThreshold.
In this case, the mResults is empty and cause crash when trying to use the first result.

Solution:
Adjust the boundary and the condition so that it can consider all size of texture.

Change-Id: Id54de57cd1501ed7355f2237f05726d2965aed6d