Copy appropriate number of rows in RecyclingClippingPixelAllocator

This is used by BitmapRegionDecoder to decode into a recycled
bitmap.

Since the specification does not guarantee that the recycled
bitmap will be larger than the decoded region, we must be careful
to only to copy min(recycledHeight, decodeHeight) rows.

This should fix flakiness in the BitmapRegionDecoderTest on cts.

BUG:26978886
Change-Id: I318468b0eaa67bd9a7860824f75d45df9bf5fbce