[HWUI] Infinite recursion in PathTessellator::recursiveQuadraticBezierVertices()

Symptom: In some cases like the distance between the calculating point is very
         small, the recursion may not terminate.
         If the calculated dx and dy are 0, d is 0 too. Then the termination
         condition(d*d < TH*TH*(dx*dx*sq + dy*dy*sq)) will never be met.
         Infinite recursion will cause stack-overflow.

Solution: We added one more threshold to terminate the recursion when d is very
          small (possibly 0).

Change-Id: I7d27a72811109766766f8f8cc5d8d88e75db7f60