Fix thumbnail resampling code to eliminate rounding errors

When resampling thumbnail image during extraction, the math logic
resulted in various rounding errors causing wrong rows/columns of
pixels to be sampled.

Replaced floating point math with integer arithmetic to remove the
rounding errors and produce exact copy of stored thumbnail when no
resampling is needed.

Change-Id: Ic80987f646c5695b4a6755bd8e7110a1a4f675b4